@Override
  public int getOperator() {
    return _is_defined ? TOK_NE : TOK_EQ;
  }
Asif : Evaluates as a filter taking advantage of indexes if appropriate. This function has a
meaningful implementation only in CompiledComparison & CompiledUndefined . It is unsupported in
other classes. The additional parameters which it takes are a boolean which is used to indicate
whether the index result set needs to be expanded to the top level or not. The second is a
CompiledValue representing the operands which are only iter evaluatable. The CompiledValue
passed will be null except if a GroupJunction has only one filter evaluatable condition & rest
are iter operands. In such cases , the iter operands will be evaluated while expanding/cutting
down the index resultset
geode-core/src/main/java/org/apache/geode/cache/query/internal/CompiledUndefined.java