@Override
    public String toString() {
      return MoreObjects.toStringHelper(this).add("operation", operation)
          .add("fromType", fromType)
          .add("fromKey", fromKey)
          .add("toKey", toKey)
          .add("deleteKey", deleteKey)
          .add("preserveEdits",preserveEdits)
          .add("defaultValue", defaultValue)
          .add("coerceTo", coerceTo)
          .add("ifKey", ifKey)
          .add("ifType", ifType)
          .add("ifValue", ifValue)
          .add("ifKeyState", ifKeyState)
          .add("keepKeys", keepKeys).omitNullValues().toString();
    }
The keys to keep when the action is {@link TransferOperation#DELETE}.
ambari-server/src/main/java/org/apache/ambari/server/stack/upgrade/ConfigUpgradeChangeDefinition.java