presto-main/src/main/java/io/prestosql/operator/EnforceSingleRowOperator.java/EnforceSingleRowOperator/EnforceSingleRowOperator
class EnforceSingleRowOperator:    public EnforceSingleRowOperator(OperatorContext operatorContext)
    {
        this.operatorContext = requireNonNull(operatorContext, "operatorContext is null");
    }