Fix save (#199)

* Fix Commit: 6ed26e1

* Update parse_encoder.dart

Fix parse encoder bug.

* Fix exception when sendSessionId is null.

* Fix GeoPoint.

* delete useless code.

Author: yulingtianxia

lib/src/objects/parse_geo_point.dart

@@ -3,33 +3,12 @@ part of flutter_parse_sdk;
 const String keyLatitude = 'latitude';
 const String keyLongitude = 'longitude';
 
-class ParseGeoPoint extends ParseObject {
+class ParseGeoPoint {
   /// Creates a Parse Object of type GeoPoint
-  ParseGeoPoint(
-      {double latitude = 0.0,
-      double longitude = 0.0,
-      bool debug,
-      ParseHTTPClient client,
-      bool autoSendSessionId})
-      : super(keyGeoPoint) {
-    this.latitude = latitude;
-    this.longitude = longitude;
+  ParseGeoPoint({this.latitude = 0.0, this.longitude = 0.0});
 
-    _debug = isDebugEnabled(objectLevelDebug: debug);
-    _client = client ??
-        ParseHTTPClient(
-            sendSessionId:
-                autoSendSessionId ?? ParseCoreData().autoSendSessionId,
-            securityContext: ParseCoreData().securityContext);
-  }
+  double latitude, longitude;
 
-  double get latitude => super.get<double>(keyLatitude);
-  set latitude(double latitude) => set<double>(keyLatitude, latitude);
-
-  double get longitude => super.get<double>(keyLongitude);
-  set longitude(double longitude) => set<double>(keyLongitude, longitude);
-
-  @override
   Map<String, dynamic> toJson({bool full = false, bool forApiRQ = false}) =>
       <String, dynamic>{
         '__type': 'GeoPoint',