diff --git a/src/main/java/org/skyscreamer/jsonassert/JSONCompareResult.java b/src/main/java/org/skyscreamer/jsonassert/JSONCompareResult.java
index 28406fbe..a8a913f4 100644
--- a/src/main/java/org/skyscreamer/jsonassert/JSONCompareResult.java
+++ b/src/main/java/org/skyscreamer/jsonassert/JSONCompareResult.java
@@ -192,13 +192,29 @@ public JSONCompareResult fail(String field, ValueMatcherException exception) {
         return this;
     }
 
+     /**CS304 Issue link: https://github.com/skyscreamer/JSONassert/issues/127
+     * modified by adding a case when {@code expected} or {@code actual} == null,
+     * which the JSON may be an invalid JSON,
+     * return a warning sentence to inform the tester.
+     */
     private String formatFailureMessage(String field, Object expected, Object actual) {
-        return field
+        String describeExp = describe(expected);
+        String describeAct = describe(actual);
+        String message = field
                 + "\nExpected: "
-                + describe(expected)
+                + describeExp
                 + "\n     got: "
-                + describe(actual)
+                + describeAct
                 + "\n";
+        if(describeExp.equals("null")){
+            message += "the expected JSON may be an invalid JSON"
+                    + "\n";
+        }
+        if(describeAct.equals("null")){
+            message += "the actual JSON may be an invalid JSON"
+                    + "\n";
+        }
+        return message;
     }
 
     /**
@@ -239,12 +255,20 @@ private String formatUnexpected(String field, Object actual) {
                 + "\n";
     }
 
+    /**CS304 Issue link: https://github.com/skyscreamer/JSONassert/issues/130
+     * modified by adding a case when {@code value} == null,
+     * return a String "null" to avoid {@exception NullPointer}
+     */
     private static String describe(Object value) {
         if (value instanceof JSONArray) {
             return "a JSON array";
         } else if (value instanceof JSONObject) {
             return "a JSON object";
-        } else {
+        }
+        else if(value == null){
+            return "null";
+        }
+        else {
             return value.toString();
         }
     }
diff --git a/src/main/java/org/skyscreamer/jsonassert/comparator/DefaultComparator.java b/src/main/java/org/skyscreamer/jsonassert/comparator/DefaultComparator.java
index bc71eae4..a612fbdf 100644
--- a/src/main/java/org/skyscreamer/jsonassert/comparator/DefaultComparator.java
+++ b/src/main/java/org/skyscreamer/jsonassert/comparator/DefaultComparator.java
@@ -47,6 +47,15 @@ public void compareJSON(String prefix, JSONObject expected, JSONObject actual, J
         }
     }
 
+
+    /**CS304 Issue link: https://github.com/skyscreamer/JSONassert/issues/130
+     * modified by adding {@code return} to the second {@code if}.
+     * because one of the {@param expectedValue} and {@param actualValue}
+     * should be null can enter the the second {@code if},
+     * after that if continue running, the next function {@code .getClass()}
+     * will always cause a {@exception NullPointer}.
+     * to avoid that case the {@code return} is added to the second {@code if}.
+     */
     @Override
     public void compareValues(String prefix, Object expectedValue, Object actualValue, JSONCompareResult result)
             throws JSONException {
@@ -55,6 +64,7 @@ public void compareValues(String prefix, Object expectedValue, Object actualValu
         }
         if ((expectedValue == null && actualValue != null) || (expectedValue != null && actualValue == null)) {
             result.fail(prefix, expectedValue, actualValue);
+            return;
         }
         if (areNumbers(expectedValue, actualValue)) {
             if (areNotSameDoubles(expectedValue, actualValue)) {