diff --git a/firestore/google/cloud/firestore.py b/firestore/google/cloud/firestore.py
index 9e0efdcb576e..4e7fd4768f13 100644
--- a/firestore/google/cloud/firestore.py
+++ b/firestore/google/cloud/firestore.py
@@ -19,7 +19,6 @@
 from google.cloud.firestore_v1beta1 import AdminClient
 from google.cloud.firestore_v1beta1 import Client
 from google.cloud.firestore_v1beta1 import CollectionReference
-from google.cloud.firestore_v1beta1 import CreateIfMissingOption
 from google.cloud.firestore_v1beta1 import DELETE_FIELD
 from google.cloud.firestore_v1beta1 import DocumentReference
 from google.cloud.firestore_v1beta1 import DocumentSnapshot
@@ -42,7 +41,6 @@
     'AdminClient',
     'Client',
     'CollectionReference',
-    'CreateIfMissingOption',
     'DELETE_FIELD',
     'DocumentReference',
     'DocumentSnapshot',
diff --git a/firestore/google/cloud/firestore_v1beta1/__init__.py b/firestore/google/cloud/firestore_v1beta1/__init__.py
index e0069d68dc0d..d8b992b1d661 100644
--- a/firestore/google/cloud/firestore_v1beta1/__init__.py
+++ b/firestore/google/cloud/firestore_v1beta1/__init__.py
@@ -22,7 +22,6 @@
 from google.cloud.firestore_v1beta1._helpers import ReadAfterWriteError
 from google.cloud.firestore_v1beta1.batch import WriteBatch
 from google.cloud.firestore_v1beta1.client import Client
-from google.cloud.firestore_v1beta1.client import CreateIfMissingOption
 from google.cloud.firestore_v1beta1.client import ExistsOption
 from google.cloud.firestore_v1beta1.client import LastUpdateOption
 from google.cloud.firestore_v1beta1.client import WriteOption
@@ -46,7 +45,6 @@
     'AdminClient',
     'Client',
     'CollectionReference',
-    'CreateIfMissingOption',
     'DELETE_FIELD',
     'DocumentReference',
     'DocumentSnapshot',
diff --git a/firestore/google/cloud/firestore_v1beta1/_helpers.py b/firestore/google/cloud/firestore_v1beta1/_helpers.py
index 3acda674b7dc..9d0cc324f3bb 100644
--- a/firestore/google/cloud/firestore_v1beta1/_helpers.py
+++ b/firestore/google/cloud/firestore_v1beta1/_helpers.py
@@ -28,10 +28,9 @@
 import grpc
 import six
 
+from google.cloud import exceptions
 from google.cloud._helpers import _datetime_to_pb_timestamp
 from google.cloud._helpers import _pb_timestamp_to_datetime
-from google.cloud import exceptions
-
 from google.cloud.firestore_v1beta1 import constants
 from google.cloud.firestore_v1beta1.gapic import enums
 from google.cloud.firestore_v1beta1.proto import common_pb2
@@ -47,10 +46,6 @@
     'The data at {!r} is not a dictionary, so it cannot contain the key {!r}')
 FIELD_PATH_DELIMITER = '.'
 DOCUMENT_PATH_DELIMITER = '/'
-_NO_CREATE_TEMPLATE = (
-    'The ``create_if_missing`` option cannot be used '
-    'on ``{}()`` requests.')
-NO_CREATE_ON_DELETE = _NO_CREATE_TEMPLATE.format('delete')
 INACTIVE_TXN = (
     'Transaction not in progress, cannot be used in API requests.')
 READ_AFTER_WRITE_ERROR = 'Attempted read after write in a transaction.'
@@ -817,7 +812,6 @@ def pbs_for_set(document_path, document_data, option):
         or two ``Write`` protobuf instances for ``set()``.
     """
     transform_paths, actual_data = remove_server_timestamp(document_data)
-
     update_pb = write_pb2.Write(
         update=document_pb2.Document(
             name=document_path,
@@ -825,7 +819,7 @@ def pbs_for_set(document_path, document_data, option):
         ),
     )
     if option is not None:
-        option.modify_write(update_pb)
+        option.modify_write(update_pb, actual_data=actual_data, path=document_path)
 
     write_pbs = [update_pb]
     if transform_paths:
@@ -856,7 +850,7 @@ def pbs_for_update(client, document_path, field_updates, option):
     """
     if option is None:
         # Default uses ``exists=True``.
-        option = client.write_option(create_if_missing=False)
+        option = client.write_option(exists=True)
 
     transform_paths, actual_updates = remove_server_timestamp(field_updates)
     update_values, field_paths = FieldPathHelper.to_field_paths(actual_updates)
@@ -870,7 +864,7 @@ def pbs_for_update(client, document_path, field_updates, option):
         update_mask=common_pb2.DocumentMask(field_paths=sorted(field_paths)),
     )
     # Due to the default, we don't have to check if ``None``.
-    option.modify_write(update_pb)
+    option.modify_write(update_pb, field_paths=field_paths)
     write_pbs = [update_pb]
 
     if transform_paths:
@@ -897,7 +891,7 @@ def pb_for_delete(document_path, option):
     """
     write_pb = write_pb2.Write(delete=document_path)
     if option is not None:
-        option.modify_write(write_pb, no_create_msg=NO_CREATE_ON_DELETE)
+        option.modify_write(write_pb)
 
     return write_pb
 
diff --git a/firestore/google/cloud/firestore_v1beta1/client.py b/firestore/google/cloud/firestore_v1beta1/client.py
index d19898bbb652..7555928af7aa 100644
--- a/firestore/google/cloud/firestore_v1beta1/client.py
+++ b/firestore/google/cloud/firestore_v1beta1/client.py
@@ -37,13 +37,15 @@
 from google.cloud.firestore_v1beta1.document import DocumentSnapshot
 from google.cloud.firestore_v1beta1.gapic import firestore_client
 from google.cloud.firestore_v1beta1.transaction import Transaction
+from google.cloud.firestore_v1beta1.proto import common_pb2
+from google.cloud.firestore_v1beta1.proto import document_pb2
+from google.cloud.firestore_v1beta1.proto import write_pb2
 
 
 DEFAULT_DATABASE = '(default)'
 """str: The default database used in a :class:`~.firestore.client.Client`."""
 _BAD_OPTION_ERR = (
-    'Exactly one of ``create_if_missing``, ``last_update_time`` '
-    'and ``exists`` must be provided.')
+    'Exactly one of ``last_update_time`` or ``exists`` must be provided.')
 _BAD_DOC_TEMPLATE = (
     'Document {!r} appeared in response but was not present among references')
 _ACTIVE_TXN = 'There is already an active transaction.'
@@ -252,10 +254,8 @@ def write_option(**kwargs):
         :meth:`~.DocumentReference.update` and
         :meth:`~.DocumentReference.delete`.
 
-        Exactly one of three keyword arguments must be provided:
+        One of the following two keyword arguments must be provided:
 
-        * ``create_if_missing`` (:class:`bool`): Indicates if the document
-          should be created if it doesn't already exist.
         * ``last_update_time`` (:class:`google.protobuf.timestamp_pb2.\
            Timestamp`): A timestamp. When set, the target document must exist
            and have been last updated at that time. Protobuf ``update_time``
@@ -268,9 +268,8 @@ def write_option(**kwargs):
         it is not allowed). Providing multiple would be an apparent
         contradiction, since ``last_update_time`` assumes that the
         document **was** updated (it can't have been updated if it
-        doesn't exist) and both ``create_if_missing`` and ``exists`` indicate
-        that it is unknown if the document exists or not (but in different
-        ways).
+        doesn't exist) and ``exists`` indicate that it is unknown if the
+        document exists or not.
 
         Args:
             kwargs (Dict[str, Any]): The keyword arguments described above.
@@ -283,12 +282,12 @@ def write_option(**kwargs):
             raise TypeError(_BAD_OPTION_ERR)
 
         name, value = kwargs.popitem()
-        if name == 'create_if_missing':
-            return CreateIfMissingOption(value)
-        elif name == 'last_update_time':
+        if name == 'last_update_time':
             return LastUpdateOption(value)
         elif name == 'exists':
             return ExistsOption(value)
+        elif name == 'merge':
+            return MergeOption()
         else:
             extra = '{!r} was provided'.format(name)
             raise TypeError(_BAD_OPTION_ERR, extra)
@@ -424,47 +423,37 @@ def modify_write(self, write_pb, **unused_kwargs):
         write_pb.current_document.CopyFrom(current_doc)
 
 
-class CreateIfMissingOption(WriteOption):
-    """Option used to assert "create if missing" on a write operation.
+class MergeOption(WriteOption):
+    """Option used to merge on a write operation.
 
     This will typically be created by
     :meth:`~.firestore_v1beta1.client.Client.write_option`.
-
-    Args:
-        create_if_missing (bool): Indicates if the document should be created
-            if it doesn't already exist.
     """
-
-    def __init__(self, create_if_missing):
-        self._create_if_missing = create_if_missing
-
-    def modify_write(self, write_pb, no_create_msg=None):
+    def modify_write(self, write_pb, actual_data=None, path=None, **unused_kwargs):
         """Modify a ``Write`` protobuf based on the state of this write option.
 
-        If:
-
-        * ``create_if_missing=False``, adds a precondition that requires
-          existence
-        * ``create_if_missing=True``, does not add any precondition
-        * ``no_create_msg`` is passed, raises an exception. For example, in a
-          :meth:`~.DocumentReference.delete`, no "create" can occur, so it
-          wouldn't make sense to "create if missing".
-
         Args:
             write_pb (google.cloud.firestore_v1beta1.types.Write): A
                 ``Write`` protobuf instance to be modified with a precondition
                 determined by the state of this option.
-            no_create_msg (Optional[str]): A message to use to indicate that
-                a create operation is not allowed.
-
-        Raises:
-            ValueError: If ``no_create_msg`` is passed.
+            actual_data (dict): 
+                The actual field names and values to use for replacing a
+                document.
+            path (str): A fully-qualified document_path
+            unused_kwargs (Dict[str, Any]): Keyword arguments accepted by
+                other subclasses that are unused here.
         """
-        if no_create_msg is not None:
-            raise ValueError(no_create_msg)
-        elif not self._create_if_missing:
-            current_doc = types.Precondition(exists=True)
-            write_pb.current_document.CopyFrom(current_doc)
+        actual_data, field_paths = _helpers.FieldPathHelper.to_field_paths(actual_data)
+        doc = document_pb2.Document(
+            name=path,
+            fields=_helpers.encode_dict(actual_data)
+        )
+        write = write_pb2.Write(
+            update=doc,
+        )
+        write_pb.CopyFrom(write)
+        mask = common_pb2.DocumentMask(field_paths=sorted(field_paths))
+        write_pb.update_mask.CopyFrom(mask)
 
 
 class ExistsOption(WriteOption):
@@ -473,24 +462,6 @@ class ExistsOption(WriteOption):
     This will typically be created by
     :meth:`~.firestore_v1beta1.client.Client.write_option`.
 
-    This option is closely related to
-    :meth:`~.firestore_v1beta1.client.CreateIfMissingOption`,
-    but a "create if missing". In fact,
-
-    .. code-block:: python
-
-       >>> ExistsOption(exists=True)
-
-    is (mostly) equivalent to
-
-    .. code-block:: python
-
-       >>> CreateIfMissingOption(create_if_missing=False)
-
-    The only difference being that "create if missing" cannot be used
-    on some operations (e.g. :meth:`~.DocumentReference.delete`)
-    while "exists" can.
-
     Args:
         exists (bool): Indicates if the document being modified
             should already exist.
diff --git a/firestore/google/cloud/firestore_v1beta1/document.py b/firestore/google/cloud/firestore_v1beta1/document.py
index 3ba6a4a82ca3..5bc4d332642d 100644
--- a/firestore/google/cloud/firestore_v1beta1/document.py
+++ b/firestore/google/cloud/firestore_v1beta1/document.py
@@ -377,9 +377,7 @@ def delete(self, option=None):
         Args:
             option (Optional[~.firestore_v1beta1.client.WriteOption]): A
                write option to make assertions / preconditions on the server
-               state of the document before applying changes. Note that
-               ``create_if_missing`` can't be used here since it does not
-               apply (i.e. a "delete" cannot "create").
+               state of the document before applying changes.
 
         Returns:
             google.protobuf.timestamp_pb2.Timestamp: The time that the delete
@@ -387,9 +385,6 @@ def delete(self, option=None):
             when the delete was sent (i.e. nothing was deleted), this method
             will still succeed and will still return the time that the
             request was received by the server.
-
-        Raises:
-            ValueError: If the ``create_if_missing`` write option is used.
         """
         write_pb = _helpers.pb_for_delete(self._document_path, option)
         with _helpers.remap_gax_error_on_commit():
diff --git a/firestore/tests/system.py b/firestore/tests/system.py
index 082e42262b43..2c32400d8879 100644
--- a/firestore/tests/system.py
+++ b/firestore/tests/system.py
@@ -139,7 +139,7 @@ def test_document_set(client, cleanup):
     cleanup(document)
 
     # 0. Make sure the document doesn't exist yet using an option.
-    option0 = client.write_option(create_if_missing=False)
+    option0 = client.write_option(exists=True)
     with pytest.raises(NotFound) as exc_info:
         document.set({'no': 'way'}, option=option0)
 
@@ -148,7 +148,7 @@ def test_document_set(client, cleanup):
 
     # 1. Use ``set()`` to create the document (using an option).
     data1 = {'foo': 88}
-    option1 = client.write_option(create_if_missing=True)
+    option1 = client.write_option(exists=False)
     write_result1 = document.set(data1, option=option1)
     snapshot1 = document.get()
     assert snapshot1.to_dict() == data1
@@ -194,6 +194,47 @@ def test_document_set(client, cleanup):
     assert exc_to_code(exc_info.value.cause) == StatusCode.FAILED_PRECONDITION
 
 
+def test_document_set_merge(client, cleanup):
+    document_id = 'for-set' + unique_resource_id('-')
+    document = client.document('i-did-it', document_id)
+    # Add to clean-up before API request (in case ``set()`` fails).
+    cleanup(document)
+
+    # 0. Make sure the document doesn't exist yet using an option.
+    option0 = client.write_option(exists=True)
+    with pytest.raises(NotFound) as exc_info:
+        document.set({'no': 'way'}, option=option0)
+
+    assert exc_info.value.message.startswith(MISSING_DOCUMENT)
+    assert document_id in exc_info.value.message
+
+    # 1. Use ``set()`` to create the document (using an option).
+    data1 = {'name': 'Sam',
+             'address': {'city': 'SF',
+                         'state': 'CA'}
+    }
+    option1 = client.write_option(exists=False)
+    write_result1 = document.set(data1, option=option1)
+    snapshot1 = document.get()
+    assert snapshot1.to_dict() == data1
+    # Make sure the update is what created the document.
+    assert snapshot1.create_time == snapshot1.update_time
+    assert snapshot1.update_time == write_result1.update_time
+
+    # 2. Call ``set()`` again to overwrite (no option).
+    data2 = {'address.city': 'LA'}
+    option2 = client.write_option(merge=True)
+    write_result2 = document.set(data2, option=option2)
+    snapshot2 = document.get()
+    assert snapshot2.to_dict() == {'name': 'Sam',
+                                   'address': {'city': 'LA',
+                                               'state': 'CA'}
+                                  }
+    # Make sure the create time hasn't changed.
+    assert snapshot2.create_time == snapshot1.create_time
+    assert snapshot2.update_time == write_result2.update_time
+
+
 def test_update_document(client, cleanup):
     document_id = 'for-update' + unique_resource_id('-')
     document = client.document('made', document_id)
@@ -207,7 +248,7 @@ def test_update_document(client, cleanup):
     assert document_id in exc_info.value.message
 
     # 1. Try to update before the document exists (now with an option).
-    option1 = client.write_option(create_if_missing=False)
+    option1 = client.write_option(exists=True)
     with pytest.raises(NotFound) as exc_info:
         document.update({'still': 'not-there'}, option=option1)
     assert exc_info.value.message.startswith(MISSING_DOCUMENT)
@@ -223,7 +264,7 @@ def test_update_document(client, cleanup):
         },
         'other': True,
     }
-    option2 = client.write_option(create_if_missing=True)
+    option2 = client.write_option(exists=False)
     write_result2 = document.update(data, option=option2)
 
     # 3. Send an update without a field path (no option).
diff --git a/firestore/tests/unit/test__helpers.py b/firestore/tests/unit/test__helpers.py
index 5669ba1da71f..e7e7a4689e0b 100644
--- a/firestore/tests/unit/test__helpers.py
+++ b/firestore/tests/unit/test__helpers.py
@@ -1172,9 +1172,9 @@ def test_without_option(self):
 
     def test_with_option(self):
         from google.cloud.firestore_v1beta1.proto import common_pb2
-        from google.cloud.firestore_v1beta1.client import CreateIfMissingOption
+        from google.cloud.firestore_v1beta1.client import ExistsOption
 
-        option = CreateIfMissingOption(False)
+        option = ExistsOption(True)
         precondition = common_pb2.Precondition(exists=True)
         self._helper(option=option, current_document=precondition)
 
@@ -1191,11 +1191,12 @@ def _call_fut(client, document_path, field_updates, option):
         return pbs_for_update(client, document_path, field_updates, option)
 
     def _helper(self, option=None, do_transform=False, **write_kwargs):
+        from google.cloud.firestore_v1beta1.client import Client
+        from google.cloud.firestore_v1beta1.client import ExistsOption
         from google.cloud.firestore_v1beta1.gapic import enums
         from google.cloud.firestore_v1beta1.proto import common_pb2
         from google.cloud.firestore_v1beta1.proto import document_pb2
         from google.cloud.firestore_v1beta1.proto import write_pb2
-        from google.cloud.firestore_v1beta1.client import Client
         from google.cloud.firestore_v1beta1.constants import SERVER_TIMESTAMP
 
         document_path = _make_ref_string(
@@ -1216,6 +1217,9 @@ def _helper(self, option=None, do_transform=False, **write_kwargs):
         map_pb = document_pb2.MapValue(fields={
             'yum': _value_pb(bytes_value=value),
         })
+        if isinstance(option, ExistsOption):
+            write_kwargs = {'current_document' : {'exists': option._exists}}
+
         expected_update_pb = write_pb2.Write(
             update=document_pb2.Document(
                 name=document_path,
@@ -1250,9 +1254,9 @@ def test_without_option(self):
 
     def test_with_option(self):
         from google.cloud.firestore_v1beta1.proto import common_pb2
-        from google.cloud.firestore_v1beta1.client import CreateIfMissingOption
+        from google.cloud.firestore_v1beta1.client import ExistsOption
 
-        option = CreateIfMissingOption(True)
+        option = ExistsOption(False)
         self._helper(option=option)
 
     def test_update_and_transform(self):
@@ -1299,16 +1303,6 @@ def test_with_option(self):
         precondition = common_pb2.Precondition(update_time=update_time)
         self._helper(option=option, current_document=precondition)
 
-    def test_bad_option(self):
-        from google.cloud.firestore_v1beta1._helpers import NO_CREATE_ON_DELETE
-        from google.cloud.firestore_v1beta1.client import CreateIfMissingOption
-
-        option = CreateIfMissingOption(True)
-        with self.assertRaises(ValueError) as exc_info:
-            self._helper(option=option)
-
-        self.assertEqual(exc_info.exception.args, (NO_CREATE_ON_DELETE,))
-
 
 class Test_get_transaction_id(unittest.TestCase):
 
diff --git a/firestore/tests/unit/test_batch.py b/firestore/tests/unit/test_batch.py
index 8f66b5211d17..59775a5f87c5 100644
--- a/firestore/tests/unit/test_batch.py
+++ b/firestore/tests/unit/test_batch.py
@@ -93,6 +93,33 @@ def test_set(self):
         )
         self.assertEqual(batch._write_pbs, [new_write_pb])
 
+    def test_set_merge(self):
+        from google.cloud.firestore_v1beta1.proto import document_pb2
+        from google.cloud.firestore_v1beta1.proto import write_pb2
+        from google.cloud.firestore_v1beta1.client import MergeOption
+
+        client = _make_client()
+        batch = self._make_one(client)
+        self.assertEqual(batch._write_pbs, [])
+
+        reference = client.document('another', 'one')
+        field = 'zapzap'
+        value = u'meadows and flowers'
+        document_data = {field: value}
+        option = MergeOption()
+        ret_val = batch.set(reference, document_data, option)
+        self.assertIsNone(ret_val)
+        new_write_pb = write_pb2.Write(
+            update=document_pb2.Document(
+                name=reference._document_path,
+                fields={
+                    field: _value_pb(string_value=value),
+                },
+            ),
+            update_mask={'field_paths':[field]}
+        )
+        self.assertEqual(batch._write_pbs, [new_write_pb])
+
     def test_update(self):
         from google.cloud.firestore_v1beta1.proto import common_pb2
         from google.cloud.firestore_v1beta1.proto import document_pb2
diff --git a/firestore/tests/unit/test_client.py b/firestore/tests/unit/test_client.py
index edb0bdfcdccf..314fc505ea6e 100644
--- a/firestore/tests/unit/test_client.py
+++ b/firestore/tests/unit/test_client.py
@@ -179,19 +179,6 @@ def test_field_path(self):
         klass = self._get_target_class()
         self.assertEqual(klass.field_path('a', 'b', 'c'), 'a.b.c')
 
-    def test_write_option_create(self):
-        from google.cloud.firestore_v1beta1.client import CreateIfMissingOption
-
-        klass = self._get_target_class()
-
-        option1 = klass.write_option(create_if_missing=False)
-        self.assertIsInstance(option1, CreateIfMissingOption)
-        self.assertFalse(option1._create_if_missing)
-
-        option2 = klass.write_option(create_if_missing=True)
-        self.assertIsInstance(option2, CreateIfMissingOption)
-        self.assertTrue(option2._create_if_missing)
-
     def test_write_option_last_update(self):
         from google.protobuf import timestamp_pb2
         from google.cloud.firestore_v1beta1.client import LastUpdateOption
@@ -234,7 +221,7 @@ def test_write_multiple_args(self):
         klass = self._get_target_class()
         with self.assertRaises(TypeError) as exc_info:
             klass.write_option(
-                create_if_missing=False,
+                exists=False,
                 last_update_time=mock.sentinel.timestamp)
 
         self.assertEqual(exc_info.exception.args, (_BAD_OPTION_ERR,))
@@ -473,59 +460,6 @@ def test_modify_write_update_time(self):
         self.assertEqual(write_pb.current_document, expected_doc)
 
 
-class TestCreateIfMissingOption(unittest.TestCase):
-
-    @staticmethod
-    def _get_target_class():
-        from google.cloud.firestore_v1beta1.client import CreateIfMissingOption
-
-        return CreateIfMissingOption
-
-    def _make_one(self, *args, **kwargs):
-        klass = self._get_target_class()
-        return klass(*args, **kwargs)
-
-    def test_constructor(self):
-        option = self._make_one(mock.sentinel.totes_bool)
-        self.assertIs(option._create_if_missing, mock.sentinel.totes_bool)
-
-    def test_modify_write_dont_create(self):
-        from google.cloud.firestore_v1beta1.proto import common_pb2
-        from google.cloud.firestore_v1beta1.proto import write_pb2
-
-        option = self._make_one(False)
-        write_pb = write_pb2.Write()
-        ret_val = option.modify_write(write_pb)
-
-        self.assertIsNone(ret_val)
-        expected_doc = common_pb2.Precondition(exists=True)
-        self.assertEqual(write_pb.current_document, expected_doc)
-
-    def test_modify_write_do_create(self):
-        from google.cloud.firestore_v1beta1.proto import write_pb2
-
-        option = self._make_one(True)
-        write_pb = write_pb2.Write()
-        ret_val = option.modify_write(write_pb)
-
-        self.assertIsNone(ret_val)
-        # No precondition is set here.
-        self.assertFalse(write_pb.HasField('current_document'))
-
-    def test_modify_write_create_not_allowed(self):
-        no_create_msg = mock.sentinel.message
-        option1 = self._make_one(True)
-        option2 = self._make_one(False)
-
-        with self.assertRaises(ValueError) as exc_info:
-            option1.modify_write(None, no_create_msg=no_create_msg)
-        self.assertEqual(exc_info.exception.args, (no_create_msg,))
-
-        with self.assertRaises(ValueError) as exc_info:
-            option2.modify_write(None, no_create_msg=no_create_msg)
-        self.assertEqual(exc_info.exception.args, (no_create_msg,))
-
-
 class TestExistsOption(unittest.TestCase):
 
     @staticmethod
diff --git a/firestore/tests/unit/test_document.py b/firestore/tests/unit/test_document.py
index 8607c6fb6a6e..5a3eb9af1bca 100644
--- a/firestore/tests/unit/test_document.py
+++ b/firestore/tests/unit/test_document.py
@@ -249,6 +249,7 @@ def _write_pb_for_set(document_path, document_data):
         )
 
     def _set_helper(self, **option_kwargs):
+        from google.cloud.firestore_v1beta1._helpers import FieldPathHelper
         # Create a minimal fake GAPIC with a dummy response.
         firestore_api = mock.Mock(spec=['commit'])
         commit_response = mock.Mock(
@@ -277,8 +278,10 @@ def _set_helper(self, **option_kwargs):
         self.assertIs(write_result, mock.sentinel.write_result)
         write_pb = self._write_pb_for_set(
             document._document_path, document_data)
+        update_values, field_paths = FieldPathHelper.to_field_paths(document_data)
+            
         if option is not None:
-            option.modify_write(write_pb)
+            option.modify_write(write_pb, field_paths=field_paths)
         firestore_api.commit.assert_called_once_with(
             client._database_string, [write_pb], transaction=None,
             options=client._call_options)
@@ -286,9 +289,6 @@ def _set_helper(self, **option_kwargs):
     def test_set(self):
         self._set_helper()
 
-    def test_set_with_option(self):
-        self._set_helper(create_if_missing=False)
-
     @staticmethod
     def _write_pb_for_update(document_path, update_values, field_paths):
         from google.cloud.firestore_v1beta1.proto import common_pb2
@@ -355,7 +355,7 @@ def test_update(self):
         self._update_helper()
 
     def test_update_with_option(self):
-        self._update_helper(create_if_missing=False)
+        self._update_helper(exists=False)
 
     def _delete_helper(self, **option_kwargs):
         from google.cloud.firestore_v1beta1.proto import write_pb2
@@ -400,13 +400,6 @@ def test_delete_with_option(self):
         )
         self._delete_helper(last_update_time=timestamp_pb)
 
-    def test_delete_with_bad_option(self):
-        from google.cloud.firestore_v1beta1._helpers import NO_CREATE_ON_DELETE
-
-        with self.assertRaises(ValueError) as exc_info:
-            self._delete_helper(create_if_missing=True)
-        self.assertEqual(exc_info.exception.args, (NO_CREATE_ON_DELETE,))
-
     def test_get_success(self):
         # Create a minimal fake client with a dummy response.
         response_iterator = iter([mock.sentinel.snapshot])