@Test(expected = RuntimeException.class)
public void testValidateOperand_keyempty() {

    Expression expression = new Expression();
    expression.setOperator(Operator.AND);
    List<Operand> operandsList = new ArrayList<>();
    Operand testOperand = new Operand();
    testOperand.setField(new Field("", "sample-app"));
    operandsList.add(testOperand);
    expression.setOperands(operandsList);
    RequestValidator.validateExpression(expression);
}