fix result if object does not contain key (fixes #270)

json-path/src/main/java/com/jayway/jsonpath/spi/json/JsonOrgJsonProvider.java

@@ -96,11 +96,10 @@ public class JsonOrgJsonProvider extends AbstractJsonProvider {
     public Object getMapValue(Object obj, String key) {
         try {
             JSONObject jsonObject = toJsonObject(obj);
-            Object o = jsonObject.get(key);
             if (!jsonObject.has(key)) {
                 return UNDEFINED;
             } else {
-                return unwrap(o);
+                return unwrap(jsonObject.get(key));
             }
         } catch (JSONException e) {
             throw new JsonPathException(e);

json-path/src/test/java/com/jayway/jsonpath/JsonOrgJsonProviderTest.java

@@ -44,4 +44,12 @@ public class JsonOrgJsonProviderTest extends BaseTest {
 
         assertThat(books.size()).isEqualTo(4);
     }
+
+    @Test
+    public void read_books_with_isbn() {
+
+        JSONArray books = using(JSON_ORG_CONFIGURATION).parse(JSON_DOCUMENT).read("$..book[?(@.isbn)]");
+
+        assertThat(books.length()).isEqualTo(2);
+    }
 }