buffer: fix isEncoding result for empty string

Author: davidtaikocha

lib/buffer.js

@@ -375,6 +375,7 @@ Buffer.compare = function compare(a, b) {
 
 Buffer.isEncoding = function(encoding) {
   return typeof encoding === 'string' &&
+         encoding.length > 0 &&
          typeof internalUtil.normalizeEncoding(encoding) === 'string';
 };
 Buffer[internalUtil.kIsEncodingSymbol] = Buffer.isEncoding;

test/parallel/test-buffer-isencoding.js

@@ -17,10 +17,13 @@ const assert = require('assert');
     assert.strictEqual(Buffer.isEncoding(enc), true);
   });
 
-[ 'utf9',
+[ '',
+  'utf9',
   'utf-7',
   'Unicode-FTW',
   'new gnu gun',
+  undefined,
+  null,
   false,
   NaN,
   {},