Merge pull request #97 from contentful/iss96

Fix NPE for null links

Author: tomxor

src/main/java/com/contentful/java/cda/ResourceUtils.java

@@ -145,6 +145,9 @@ static void resolveSingleLink(CDAEntry entry, CDAField field, ArrayResource arra
   }
 
   static String getLinkId(Object link) {
+    if (link == null) {
+      return null;
+    }
     if (link instanceof CDAResource) {
       // already resolved
       return ((CDAResource) link).id();

src/test/java/com/contentful/java/cda/LinkTest.java

@@ -50,4 +50,13 @@ public class LinkTest extends BaseTest {
 
     assertThat((List<String>) container.getField("symbols")).containsExactly("a", "b", "c");
   }
+
+  @Test @Enqueue(defaults = {
+      "links/space.json",
+      "links/content_types.json"
+  }, value = {
+      "links/sync_empty_links.json"
+  }) public void testEmptyLinks() throws Exception {
+    client.sync().fetch();
+  }
 }

src/test/resources/links/sync_empty_links.json

@@ -0,0 +1,47 @@
+{
+  "sys": {
+    "type": "Array"
+  },
+  "items": [
+    {
+      "sys": {
+        "space": {
+          "sys": {
+            "type": "Link",
+            "linkType": "Space",
+            "id": "75oea9kejr52"
+          }
+        },
+        "type": "Entry",
+        "contentType": {
+          "sys": {
+            "type": "Link",
+            "linkType": "ContentType",
+            "id": "2s9novBkP2G0oasUaG8kCs"
+          }
+        },
+        "id": "3vyEoAvlkk8yE4a8gCCkiu",
+        "revision": 1,
+        "createdAt": "2015-07-10T11:56:10.469Z",
+        "updatedAt": "2015-07-10T11:56:10.469Z"
+      },
+      "fields": {
+        "entry": {
+          "en-US": null
+        },
+        "asset": {
+          "en-US": null
+        },
+        "entries": {
+          "en-US": []
+        },
+        "assets": {
+          "en-US": []
+        },
+        "symbols": {
+          "en-US": []
+        }
+      }
+    }
+  ]
+}