Return a "JsonNull" object for empty whitespace input into the JsonParser.

gson/src/main/java/com/google/gson/JsonParser.java

@@ -63,7 +63,7 @@ public final class JsonParser {
       throw new JsonParseException("Failed parsing JSON source: " + json + " to Json", e);
     } catch (JsonParseException e) {
       if (e.getCause() instanceof EOFException) {
-        return null;
+        return JsonNull.createJsonNull();
       } else {
         throw e;
       }

gson/src/test/java/com/google/gson/JsonParserTest.java

@@ -46,6 +46,17 @@ public class JsonParserTest extends TestCase {
     assertEquals(10, e.getAsJsonObject().get("a").getAsInt());
     assertEquals("c", e.getAsJsonObject().get("b").getAsString());
   }
+  
+  public void testParseEmptyString() {
+    JsonElement e = parser.parse("\"   \"");
+    assertTrue(e.isJsonPrimitive());
+    assertEquals("   ", e.getAsString());
+  }
+
+  public void testParseEmptyWhitespaceInput() {
+    JsonElement e = parser.parse("     ");
+    assertTrue(e.isJsonNull());
+  }
 
   public void testParseReader() {
     StringReader reader = new StringReader("{a:10,b:'c'}");