public static Expression simplifyPredicate(Expression predicate) {
    return new PredicateSimplifier().process(predicate, null);
  }
Simplify the given predicate (Remove the NULL and TRUE/FALSE expression).

@param predicate given predicate
@return the predicate after simplifying
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/analyze/PredicateUtils.java