Nullable and error report in useCase

[pro100svitlo]

So i found 2 bugs in the use_case related section, both related to the nullable values:

№1

_appThemeHandler = consume(_listenAppThemeUseCase, initialData: none);

consume method receive optional but nullable param initialData.
the problem comes, when useCase input is not nullable.

№2

  useCaseTest<ListenAppThemeUseCase, void, AppTheme>(
    'WHEN storage emit new value THEN useCase emit it as well',
    build: () => useCase,
    setUp: () {
      controller.add(AppTheme.dark);
      controller.close();
    },
    input: [null],
    expect: [useCaseSuccess(AppTheme.dark)],
  );

same thing here, but even worse a bit.
input can receive a list of values. it might be null (as in the example), but the useCase does not accept nullable values.
So in the current setup error will be swallowed by some internal try/catch (probably line 92, use_case_test.dart) and never returned,
The test continues to execute (transaction never called properly cos of the null value) and as result - timeout exception comes

[frankpepermans]

The try catch should be removed in the other PR,

For initialdata, will check