unnecessary_null_comparison

The operand can't be 'null', so the condition is always 'false'.

The operand can't be 'null', so the condition is always 'true'.

The operand must be 'null', so the condition is always 'false'.

The operand must be 'null', so the condition is always 'true'.

The analyzer produces this diagnostic when it finds an equality comparison (either == or !=) with one operand of null and the other operand can't be null. Such comparisons are always either true or false, so they serve no purpose.

The following code produces this diagnostic because x can never be null, so the comparison always evaluates to true:

void f(int x) {
  if (x != null) {
    print(x);
  }
}

The following code produces this diagnostic because x can never be null, so the comparison always evaluates to false:

void f(int x) {
  if (x == null) {
    throw ArgumentError("x can't be null");
  }
}

If the other operand should be able to be null, then change the type of the operand:

void f(int? x) {
  if (x != null) {
    print(x);
  }
}

If the other operand really can't be null, then remove the condition:

void f(int x) {
  print(x);
}