unnecessary_null_assert_pattern

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

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

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

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

Remove the null-assert pattern:

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