Merge pull request yahoo#478 from yahoo/adding-ddi-support

Adding prefabricated check

elide-annotations/src/main/java/com/yahoo/elide/security/checks/prefab/Common.java

@@ -10,7 +10,6 @@
 import com.yahoo.elide.security.PersistentResource;
 import com.yahoo.elide.security.RequestScope;
 import com.yahoo.elide.security.checks.CommitCheck;
-
 import java.util.Optional;
 
 /**
@@ -34,4 +33,16 @@ public boolean ok(T record, RequestScope requestScope, Optional<ChangeSpec> chan
             return false;
         }
     }
+
+    /**
+     * A check that enables Only teh removal of an object from a relationship.
+     * @param <T> the type of object that this check guards
+     */
+    public static class FieldSetToNull<T> extends CommitCheck<T> {
+        @Override
+        public boolean ok(T record, RequestScope requestScope, Optional<ChangeSpec> changeSpec) {
+            return changeSpec.map((c) -> { return c.getOriginal() != null && c.getModified() == null; })
+                    .orElse(false);
+        }
+    }
 }