code: public Criteria function(Function function) {
  		Assert.notNull(function, "Cannot add 'null' function to criteria.");
  		predicates.add(new Predicate(OperationKey.FUNCTION, function));
  		return this;
  	}
docs: Creates {@link Predicate} for given {@link Function}.
  
  @param function must not be null
  @return
  @throws IllegalArgumentException if function is null
  @since 1.1