The left operand can't be null, so the right operand is never executedDRT-W1287

The analyzer produces this diagnostic in two cases.

The first is when the left operand of an ?? operator can't be null. The right operand is only evaluated if the left operand has the value null, and because the left operand can't be null, the right operand is never evaluated.

The second is when the left-hand side of an assignment using the ??= operator can't be null. The right-hand side is only evaluated if the left-hand side has the value null, and because the left-hand side can't be null, the right-hand side is never evaluated.

Examples

The following code produces this diagnostic because x can't be null:

int f(int x) {
  return x ?? 0;
}

The following code produces this diagnostic because f can't be null:

class C {
  int f = -1;

  void m(int x) {
    f ??= x;
  }
}

Common fixes

If the diagnostic is reported for an ?? operator, then remove the ?? operator and the right operand:

int f(int x) {
  return x;
}

If the diagnostic is reported for an assignment, and the assignment isn't needed, then remove the assignment:

class C {
  int f = -1;

  void m(int x) {
  }
}

If the assignment is needed, but should be based on a different condition, then rewrite the code to use = and the different condition:

class C {
  int f = -1;

  void m(int x) {
    if (f < 0) {
      f = x;
    }
  }
}