Exclude null query vars by default and add new @Method annotation includeNullQueryVars

[techouse]

Fix #371

Because some backends do not ignore null query parameters I have re-introduced the behaviour of excluding null query vars by default. This includes nested null query parameters inside maps.

This was the default behaviour prior to v5.0.1 and the merge of #364.

Additionally, I have added a @Method annotation bool includeNullQueryVars which, if set to true, includes null query parameters when encoding them into the URL query.

• Example with includeNullQueryVars: false (default; same behaviour as before v5.0.1)

  @Get(path: '/get_data')
  Future<Response<String>> getData({
    @Query('foo') String? foo,
    @Query('bar') String? bar,
    @Query('baz') String? baz,
  });
  
  final response = await service.getData(
    foo: 'foo_val',
    baz: 'baz_val',
  );

  Produces /test/get_data&foo=foo_val&baz=baz_val

• Example with includeNullQueryVars: true (the current default in v5.0.1)

  @Get(
    path: '/get_data', 
    includeNullQueryVars: true,
  )
  Future<Response<String>> getData({
    @Query('foo') String? foo,
    @Query('bar') String? bar,
    @Query('baz') String? baz,
  });
  
  final response = await service.getData(
    foo: 'foo_val',
    baz: 'baz_val',
  );

  Produces /test/get_data&foo=foo_val&bar=&baz=baz_val

NOTE: Empty Strings are always included. If you do not want them to be included make them nullable, i.e. String?

@Get(path: '/get_data')
Future<Response<String>> getData({
  @Query('foo') String foo = '',
  @Query('bar') String? bar,
  @Query('baz') String? baz,
});

final response = await service.getData(
  bar: null,
  baz: 'baz_val',
);

Produces /test/get_data&foo=&baz=baz_val

NOTE 2: null values and empty Strings inside query Lists are always excluded.

@Get(path: '/get_data')
Future<Response<String>> getData({
  @Query('foo') List<String?> foo,
});

final response = await service.getData(
  foo: <String?>[
    'value1', 
    '', 
    null, 
    'value4',
  ],
);

Produces /test/get_data&foo=value1&foo=value4

[luis901101]

Hi and thanks for this fix, I also think that default should be ignoreNullQueryVars: true and not otherwise, because as you commented this was the default behavior prior to v5.0.1, so I think it is better to keep the same default to maintain backward compatibility otherwise this will break some existing projects requests, like it's currently happening to me using Java Jooby as Backend.
Not ignoring null query vars as default could be for a new breaking change version like v6.0.0, but I think for v5.x.x the default behavior should remain the same.

[techouse]

Not ignoring null query vars as default could be for a new breaking change version like v6.0.0, but I think for v5.x.x the default behavior should remain the same.

Agreed. I'll amend it.

[techouse]

I have renamed ignoreNullQueryVars to includeNullQueryVars. The default for this setting is false, meaning that the default behaviour will be reverted to the one before v5.0.1.

NOTE: Empty strings are always included.

NOTE 2: null values and empty Strings inside query Lists are always excluded.

I'll now amend the PR description.

[JEuler]

Hehe)

[JEuler]

LGTM, great work as always, thank you so much! ❤️