Merge branch 'master' of github.com:swagger-api/swagger-core

Author: fehguy

modules/swagger-models/src/main/java/io/swagger/models/properties/RefProperty.java

@@ -58,12 +58,20 @@ public void setType(String type) {
 
     @JsonIgnore
     public RefFormat getRefFormat() {
-        return this.genericRef.getFormat();
+        if (genericRef != null) {
+            return this.genericRef.getFormat();
+        } else {
+            return null;
+        }
     }
 
     @JsonIgnore
     public String getSimpleRef() {
-        return genericRef.getSimpleRef();
+        if (genericRef != null) {
+            return this.genericRef.getSimpleRef();
+        } else {
+            return null;
+        }
     }
 
     @Override
@@ -92,4 +100,4 @@ public boolean equals(Object obj) {
         }
         return true;
     }
-}
+}