fixed keeping null as string

Author: marilynel

src/main/java/org/json/XML.java

@@ -428,6 +428,9 @@ private static boolean parse(XMLTokener x, JSONObject context, String name, XMLP
                                                 config.isKeepNumberAsString()
                                                         ? ((String) token)
                                                         : obj);
+                                    } else if (obj == JSONObject.NULL) {
+                                        jsonObject.accumulate(config.getcDataTagName(),
+                                                config.isKeepStrings() ? ((String) token) : obj);
                                     } else {
                                         jsonObject.accumulate(config.getcDataTagName(), stringToValue((String) token));
                                     }

src/test/java/org/json/junit/XMLConfigurationTest.java

@@ -794,6 +794,18 @@ public void testToJSONArray_jsonOutput_withKeepBooleanAsString() {
         Util.compareActualVsExpectedJsonObjects(actualJsonOutput,expected);
     }
 
+    /**
+     * null is "null" when keepStrings == true
+     */
+    @Test
+    public void testToJSONArray_jsonOutput_null_withKeepString() {
+        final String originalXml = "<root><id>01</id><id>1</id><id>00</id><id>0</id><item id=\"01\"/><title>null</title></root>";
+        final JSONObject expected = new JSONObject("{\"root\":{\"item\":{\"id\":\"01\"},\"id\":[\"01\",\"1\",\"00\",\"0\"],\"title\":\"null\"}}");
+        final JSONObject actualJsonOutput = XML.toJSONObject(originalXml,
+                new XMLParserConfiguration().withKeepStrings(true));
+        Util.compareActualVsExpectedJsonObjects(actualJsonOutput,expected);
+    }
+
     /**
      * Test keepStrings behavior when setting keepBooleanAsString, keepNumberAsString
      */