public static Specification<PerfTest> scheduledTimeNotEmptyPredicate() {
		return (Specification<PerfTest>) (root, query, cb) -> root.get("scheduledTime").isNotNull();
	}
Get the Specification which provide empty predicate for schedule time. This is for the base element for "and" or
"or" combination.

@return {@link Specification}
ngrinder-controller/src/main/java/org/ngrinder/perftest/repository/PerfTestSpecification.java