Update firebase-firestore/src/main/java/com/google/firebase/firestore/model/ObjectValue.java

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: MarkDuckworth

firebase-firestore/src/main/java/com/google/firebase/firestore/model/ObjectValue.java

@@ -131,8 +131,8 @@ private Value buildProto() {
         MapValue mergedResult = applyOverlayLocked(FieldPath.EMPTY_PATH, overlayMap);
         if (mergedResult != null) {
           partialValue = Value.newBuilder().setMapValue(mergedResult).build();
-          overlayMap.clear();
         }
+        overlayMap.clear();
       }
     }
     return partialValue;