dartdart-analyzer

dart: unnecessary_null_comparision

For the following code:

bool assertTest(int? n1, int? n2) {
  return (n1 == null) || (n1 != null && n2 != null);
}

there is a warning at n1 != null saying The operand can't be null, so the condition is always true. Why does this warning show up? n1 is obviously nullable.

Solution

  • The boolean operation are lazy, it means that if you evaluate a || b and a is true, then b is not even evaluated.

    In your case, if b = (n1 != null && n2 != null) is evaluated, it means a = (n1 == null) = false, which means n1 != null so the check n1 != null will always be true.