Fix NotInFilter matching (#1947)

Author: Brian Chen

firebase-firestore/src/androidTest/java/com/google/firebase/firestore/QueryTest.java

@@ -659,7 +659,7 @@ public void testQueriesCanUseNotInFilters() {
     // With Null.
     List<Object> nullArray = new ArrayList<>();
     nullArray.add(null);
-    snapshot = waitFor(collection.whereNotIn("key", nullArray).get());
+    snapshot = waitFor(collection.whereNotIn("zip", nullArray).get());
     assertEquals(new ArrayList<>(), querySnapshotToValues(snapshot));
 
     // With NaN.

firebase-firestore/src/main/java/com/google/firebase/firestore/core/NotInFilter.java

@@ -30,6 +30,9 @@ public class NotInFilter extends FieldFilter {
 
   @Override
   public boolean matches(Document doc) {
+    if (Values.contains(getValue().getArrayValue(), Values.NULL_VALUE)) {
+      return false;
+    }
     Value other = doc.getField(getField());
     return other != null && !Values.contains(getValue().getArrayValue(), other);
   }

firebase-firestore/src/test/java/com/google/firebase/firestore/remote/RemoteSerializerTest.java

@@ -84,9 +84,11 @@
 import com.google.firestore.v1.Write;
 import com.google.protobuf.ByteString;
 import com.google.protobuf.Int32Value;
+import com.google.protobuf.NullValue;
 import com.google.protobuf.Timestamp;
 import com.google.type.LatLng;
 import io.grpc.Status;
+import java.util.ArrayList;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.List;
@@ -706,6 +708,31 @@ public void testNotInSerialization() {
     assertTrue(roundTripped instanceof NotInFilter);
   }
 
+  @Test
+  public void testNotInWithNullSerialization() {
+    List<Object> nullArray = new ArrayList<>();
+    nullArray.add(null);
+    FieldFilter inputFilter = filter("field", "not-in", nullArray);
+    StructuredQuery.Filter apiFilter = serializer.encodeUnaryOrFieldFilter(inputFilter);
+
+    ArrayValue.Builder notInFilterValue =
+        ArrayValue.newBuilder().addValues(Value.newBuilder().setNullValue(NullValue.NULL_VALUE));
+    StructuredQuery.Filter expectedFilter =
+        Filter.newBuilder()
+            .setFieldFilter(
+                StructuredQuery.FieldFilter.newBuilder()
+                    .setField(FieldReference.newBuilder().setFieldPath("field"))
+                    .setOp(Operator.NOT_IN)
+                    .setValue(Value.newBuilder().setArrayValue(notInFilterValue))
+                    .build())
+            .build();
+
+    assertEquals(expectedFilter, apiFilter);
+    FieldFilter roundTripped = serializer.decodeFieldFilter(apiFilter.getFieldFilter());
+    assertEquals(roundTripped, inputFilter);
+    assertTrue(roundTripped instanceof NotInFilter);
+  }
+
   @Test
   public void testArrayContainsAnySerialization() {
     FieldFilter inputFilter = filter("field", "array-contains-any", asList(42));