fix a bug in handling of null values in transformers

Author: jtnelson

src/main/java/com/cinchapi/etl/Transformer.java

@@ -98,8 +98,7 @@ public default Map<String, Object> transform(Map<String, Object> object) {
         object.forEach((key, value) -> {
             Map<String, Object> data = transform(key, value);
             data = data == null ? AnyMaps.create(key, value) : data;
-            data.forEach(
-                    (k, v) -> transformed.merge(k, v, MergeStrategies::upsert));
+            AnyMaps.mergeInPlace(transformed, data, MergeStrategies::upsert);
         });
         return transformed;
     }

src/test/java/com/cinchapi/etl/TransformersTest.java

@@ -21,6 +21,7 @@
 import org.junit.Assert;
 import org.junit.Test;
 
+import com.cinchapi.common.collect.AnyMaps;
 import com.cinchapi.common.describe.Empty;
 import com.cinchapi.concourse.Tag;
 import com.cinchapi.concourse.util.Random;
@@ -139,5 +140,13 @@ public void testValueRemoveIfEmpty() {
         Assert.assertEquals(ImmutableMap.of(), Transformers.removeValuesThatAre(empty)
                 .transform("foo", (Object) "   "));
     }
+    
+    @Test
+    public void testNullValueHandling() {
+        Transformer transformer = Transformers.noOp();
+        Map<String, Object> expected = AnyMaps.create("foo", null);
+        Map<String, Object> actual = transformer.transform(expected);
+        Assert.assertEquals(expected, actual);
+    }
 
 }