unnecessary_null_check_pattern

The null-check pattern will have no effect because the matched type isn't nullable.

The analyzer produces this diagnostic when a null-check pattern is used to match a value that isn't nullable.

The following code produces this diagnostic because the value x isn't nullable:

void f(int x) {
  if (x case var a? when a > 0) {}
}

Remove the null-check pattern:

void f(int x) {
  if (x case var a when a > 0) {}
}