fixing #271

Author: erosb

core/src/main/java/org/everit/json/schema/loader/ReferenceLookup.java

@@ -91,10 +91,12 @@ Map<String, Object> withoutRef(JsonObject original) {
     }
 
     private JsonObject lookupObjById(JsonValue val, String idAttrVal) {
+        String idKeyword = val.ls.specVersion().idKeyword();
         if (val instanceof JsonObject) {
             JsonObject obj = (JsonObject) val;
-            if (obj.containsKey("$id") && obj.require("$id").requireString()
-                    .equals(idAttrVal)) {
+            if (obj.containsKey(idKeyword)
+                    && obj.require(idKeyword).typeOfValue() == String.class
+                    && obj.require(idKeyword).requireString().equals(idAttrVal)) {
                 return obj;
             }
             for (String key : obj.keySet()) {

tests/vanilla/src/main/resources/org/everit/json/schema/issues/issue271/remotes/dummy-schema.json

@@ -0,0 +1 @@
+{}