code: @FormatMethod
    public final void checkAssignableTo(Type expected, String fmt, Object... args) {
      if (Flags.DEBUG && !BytecodeUtils.isPossiblyAssignableFrom(expected, resultType())) {
        String message =
            String.format(
                "Type mismatch. %s not assignable to %s.",
                resultType().getClassName(), expected.getClassName());
        if (!fmt.isEmpty()) {
          message = String.format(fmt, args) + ". " + message;
        }
  
        throw new IllegalArgumentException(message);
      }
    }
docs: Check that this expression is assignable to {@code expected}.