[GH-3202] Handle empty Geography inputs in ST_MakeLine

common/src/main/java/org/apache/sedona/common/geography/Functions.java

@@ -214,7 +214,8 @@ public static Double y(Geography g) {
    * measurement functions. No CRS transformation or SRID compatibility check is performed; if the
    * inputs have different SRIDs, the first input's SRID is used. When the second input is a
    * LineString whose first coordinate equals the current endpoint, that seam coordinate is added
-   * only once. Point and MultiPoint coordinates are always retained.
+   * only once. Point and MultiPoint coordinates are always retained. Empty inputs contribute no
+   * coordinates; when exactly one coordinate remains, it is repeated to form a valid LineString.
    */
   public static Geography makeLine(Geography g1, Geography g2) {
     if (g1 == null || g2 == null) return null;
@@ -251,6 +252,11 @@ private static Geometry makeLineGeometry(Geometry first, Geometry second) {
       coordinates.add(appended[i]);
     }
 
+    // PostGIS and SedonaDB skip empty components. JTS cannot represent their one-coordinate
+    // LineString result, so repeat that coordinate while preserving the same point set.
+    if (coordinates.size() == 1) {
+      coordinates.add(new Coordinate(coordinates.get(0)));
+    }
     return first.getFactory().createLineString(coordinates.toArray(new Coordinate[0]));
   }
 

common/src/test/java/org/apache/sedona/common/Geography/FunctionTest.java

@@ -235,6 +235,33 @@ public void makeLine_coincidentPointsRemainUsableAfterWKBRoundTrip() throws Pars
     assertEquals(3, Functions.nPoints(extended));
   }
 
+  @Test
+  public void makeLine_skipsEmptyInputsAndNormalizesSingleCoordinate() throws ParseException {
+    Geography emptyPoint = Constructors.geogFromWKT("POINT EMPTY", 3857);
+    Geography emptyLine = Constructors.geogFromWKT("LINESTRING EMPTY", 4326);
+    Geography emptyMultiPoint = Constructors.geogFromWKT("MULTIPOINT EMPTY", 4326);
+    Geography point = Constructors.geogFromWKT("POINT (12 34)", 4326);
+
+    Geography onlySecond = roundTripWKB(Functions.makeLine(emptyPoint, point));
+    assertEquals("LINESTRING (12 34, 12 34)", Functions.asText(onlySecond));
+    assertEquals(2, Functions.nPoints(onlySecond));
+    assertEquals(3857, onlySecond.getSRID());
+
+    Geography onlyFirst = roundTripWKB(Functions.makeLine(point, emptyLine));
+    assertEquals("LINESTRING (12 34, 12 34)", Functions.asText(onlyFirst));
+    assertEquals(2, Functions.nPoints(onlyFirst));
+    assertEquals(4326, onlyFirst.getSRID());
+
+    Geography afterEmptyMultiPoint = roundTripWKB(Functions.makeLine(emptyMultiPoint, point));
+    assertEquals("LINESTRING (12 34, 12 34)", Functions.asText(afterEmptyMultiPoint));
+    assertEquals(2, Functions.nPoints(afterEmptyMultiPoint));
+
+    Geography noCoordinates = roundTripWKB(Functions.makeLine(emptyPoint, emptyLine));
+    assertEquals("LINESTRING EMPTY", Functions.asText(noCoordinates));
+    assertEquals(0, Functions.nPoints(noCoordinates));
+    assertEquals(3857, noCoordinates.getSRID());
+  }
+
   @Test
   public void makeLine_deduplicatesLineStringSeamAndPreservesOtherRepeats() throws ParseException {
     Geography first = Constructors.geogFromWKT("LINESTRING (0 0, 1 0)", 4326);

docs/api/flink/Geography-Functions/ST_MakeLine.md

@@ -29,7 +29,7 @@ Return type: `Geography`
 
 Since: `v1.9.1`
 
-Only the two-argument signature accepts Geography inputs. The array form of `ST_MakeLine` remains Geometry-only. Repeated and coincident Point or MultiPoint coordinates are preserved. When the second input is a LineString whose first coordinate matches the current endpoint, that seam coordinate appears only once.
+Only the two-argument signature accepts Geography inputs. The array form of `ST_MakeLine` remains Geometry-only. Repeated and coincident Point or MultiPoint coordinates are preserved. When the second input is a LineString whose first coordinate matches the current endpoint, that seam coordinate appears only once. Empty inputs contribute no coordinates. If exactly one coordinate remains, it is repeated to produce a valid LineString.
 
 The output copies the first input's SRID without transforming either input or validating that their SRIDs match. If the inputs have different SRIDs, the second input's SRID is ignored. An SRID of `0` on the first input remains `0`.
 

docs/api/sql/geography/Geography-Functions/ST_MakeLine.md

@@ -29,7 +29,7 @@ Return type: `Geography`
 
 Since: `v1.9.1`
 
-Only the two-argument signature accepts Geography inputs. The array/aggregate form of `ST_MakeLine` remains Geometry-only. Repeated and coincident Point or MultiPoint coordinates are preserved. When the second input is a LineString whose first coordinate matches the current endpoint, that seam coordinate appears only once.
+Only the two-argument signature accepts Geography inputs. The array/aggregate form of `ST_MakeLine` remains Geometry-only. Repeated and coincident Point or MultiPoint coordinates are preserved. When the second input is a LineString whose first coordinate matches the current endpoint, that seam coordinate appears only once. Empty inputs contribute no coordinates. If exactly one coordinate remains, it is repeated to produce a valid LineString.
 
 The output copies the first input's SRID without transforming either input or validating that their SRIDs match. If the inputs have different SRIDs, the second input's SRID is ignored. An SRID of `0` on the first input remains `0`.
 

flink/src/test/java/org/apache/sedona/flink/GeographyFunctionTest.java

@@ -137,6 +137,27 @@ public void testMakeLinePreservesCoincidentPointsAndFirstSRID() throws Exception
     }
   }
 
+  @Test
+  public void testMakeLineSkipsEmptyGeographyInputs() throws Exception {
+    Table table =
+        tableEnv.sqlQuery(
+            "SELECT "
+                + "ST_AsText(ST_MakeLine("
+                + "ST_GeogFromWKT('POINT EMPTY', 3857), "
+                + "ST_GeogFromWKT('POINT (12 34)', 4326))) AS empty_first, "
+                + "ST_AsText(ST_MakeLine("
+                + "ST_GeogFromWKT('POINT (12 34)', 4326), "
+                + "ST_GeogFromWKT('LINESTRING EMPTY', 3857))) AS empty_second, "
+                + "ST_AsEWKT(ST_MakeLine("
+                + "ST_GeogFromWKT('POINT EMPTY', 3857), "
+                + "ST_GeogFromWKT('LINESTRING EMPTY', 4326))) AS both_empty");
+
+    Row row = first(table);
+    assertEquals("LINESTRING (12 34, 12 34)", row.getFieldAs("empty_first"));
+    assertEquals("LINESTRING (12 34, 12 34)", row.getFieldAs("empty_second"));
+    assertEquals("SRID=3857; LINESTRING EMPTY", row.getFieldAs("both_empty"));
+  }
+
   @Test
   public void testDistance() throws Exception {
     String wktA = "POINT (0 0)";

spark/common/src/test/scala/org/apache/sedona/sql/geography/GeographyFunctionTest.scala

@@ -259,6 +259,30 @@ class GeographyFunctionTest extends TestBaseScala {
       assertEquals("SRID=4326; LINESTRING (0 0, 1 0, 2 0)", repeated.getString(1))
       assertEquals(3, repeated.getInt(2))
     }
+
+    it("ST_MakeLine skips empty geography inputs") {
+      val row = sparkSession
+        .sql("""
+          SELECT
+            ST_AsText(ST_MakeLine(
+              ST_GeogFromWKT('POINT EMPTY', 3857),
+              ST_GeogFromWKT('POINT (12 34)', 4326)
+            )) AS empty_first,
+            ST_AsText(ST_MakeLine(
+              ST_GeogFromWKT('POINT (12 34)', 4326),
+              ST_GeogFromWKT('LINESTRING EMPTY', 3857)
+            )) AS empty_second,
+            ST_AsEWKT(ST_MakeLine(
+              ST_GeogFromWKT('POINT EMPTY', 3857),
+              ST_GeogFromWKT('LINESTRING EMPTY', 4326)
+            )) AS both_empty
+        """)
+        .first()
+
+      assertEquals("LINESTRING (12 34, 12 34)", row.getString(0))
+      assertEquals("LINESTRING (12 34, 12 34)", row.getString(1))
+      assertEquals("SRID=3857; LINESTRING EMPTY", row.getString(2))
+    }
   }
 
   // ─── Level 2: ST_Length, ST_Area, ST_Distance ──────────────────────────