mapToQuery changes

[techouse]

This PR will require a bit of discussion:

• I changed how empty strings and null are encoded into the query string.

  I've never seen query parameters taken out if their values were empty or null if they were provided to the method encoding the map and I think it's up to the user to clean them up explicitly as most APIs simply ignore them.
  For comparison, Python's urllib.parse.urlencode employs the same logic.

  // before
  print(mapToQuery({'foo': ''})); // prints ''
  // after
  print(mapToQuery({'foo': ''})); // prints 'foo='
  
  // before
  print(mapToQuery({'foo': null})); // prints ''
  // after
  print(mapToQuery({'foo': null})); // prints 'foo='

• I changed how empty strings and null inside Lists are encoded into query strings.

  Since these values here are packed into a List I'm not sure why they should be encoded, so I removed them (essentially the reverse of the bullet point above which targets standalone values). A query like this is more or less used for filtering by multiple IDs or equivalent where an empty param might actually be detrimental.

  // before
  print(mapToQuery('foo': ['', 'baz', 'etc'])); // prints 'foo=&foo=baz&foo=etc'
  // after
  print(mapToQuery('foo': ['', 'baz', 'etc'])); // prints 'foo=baz&foo=etc'
  
  // before
  print(mapToQuery('foo': [null, 'baz', 'etc'])); // prints 'foo=&foo=baz&foo=etc'
  // after
  print(mapToQuery('foo': [null, 'baz', 'etc'])); // prints 'foo=baz&foo=etc'

• I made _normalizeValue null-safe. Now it will encode null to '' rather than explode violently 😅

• I added the option to use square brackets [ ] as an encoded query list and map separator.

  Currently, they are hardcoded to dots ., and it's already been expressed that more flexibility is needed QueryMap buildUrl  #301.
  So I've added an optional Method annotation bool useBrackets.

  // using this input in both instances
  final Map<String, dynamic> input = {
     'bar': 'baz',
     'zap': 'abc',
     'etc': {
       'abc': 'def',
       'ghi': 'jkl',
       'mno': {
         'opq': 'rst',
         'uvw': 'xyz',
         'list': ['a', 123, false],
       },
     },
   };
  
  // the default way using dots as query map separators
  @Get(path: '/map_query_param')
  Future<Response<String>> getUsingMapQueryParam(
    @Query('value') Map<String, dynamic> value,
  );
  
  // the above produces a URL like this (the line breaks are there just for readability)
  //
  // /test/map_query_param
  // ?value.bar=baz
  // &value.zap=abc
  // &value.etc.abc=def
  // &value.etc.ghi=jkl
  // &value.etc.mno.opq=rst
  // &value.etc.mno.uvw=xyz
  // &value.etc.mno.list=a
  // &value.etc.mno.list=123
  // &value.etc.mno.list=false
  
  // specifying queryMapSeparator: 'brackets'
  @Get(path: '/map_query_param_with_brackets', useBrackets: true)
  Future<Response<String>> getUsingMapQueryParamWithBrackets(
    @Query('value') Map<String, dynamic> value,
  );
  
  // this produces a URL like this (the line breaks are there just for readability)
  //
  // /test/map_query_param_with_brackets
  // ?value%5Bbar%5D=baz
  // &value%5Bzap%5D=abc
  // &value%5Betc%5D%5Babc%5D=def
  // &value%5Betc%5D%5Bghi%5D=jkl
  // &value%5Betc%5D%5Bmno%5D%5Bopq%5D=rst
  // &value%5Betc%5D%5Bmno%5D%5Buvw%5D=xyz
  // &value%5Betc%5D%5Bmno%5D%5Blist%5D%5B%5D=a
  // &value%5Betc%5D%5Bmno%5D%5Blist%5D%5B%5D=123
  // &value%5Betc%5D%5Bmno%5D%5Blist%5D%5B%5D=false
  //
  // URI decoded this reads as:
  //
  // /test/map_query_param_with_brackets
  // ?value[bar]=baz
  // &value[zap]=abc
  // &value[etc][abc]=def
  // &value[etc][ghi]=jkl
  // &value[etc][mno][opq]=rst
  // &value[etc][mno][uvw]=xyz
  // &value[etc][mno][list][]=a
  // &value[etc][mno][list][]=123
  // &value[etc][mno][list][]=false 

And of course, I've added a tonne of tests ✅

Check chopper/tests/utils_test.dart for more examples

[JEuler]

Oh my god, this is really cool! Thank you so much, I agree that we should not ignore the null params silently, and should just pass it as it is.

I saw your request about "hey man release to master" - let's do this after that PR merge. Do you have any plans to add more code here? :)

[techouse]

Do you have any plans to add more code here? :)

I think one more thing.... Gimme 15min

[techouse]

Done. I added the option to also use brackets in lists, e.g

hxxp://path/to/script?foo[]=123&foo[]=456&foo[]=789

As that is also one of the ways some backends parse lists (this is the standard in PHP, for example).

[JEuler]

I will prepare the PR to master soon, maybe today, maybe tomorrow morning. Thank you very much for contributing! Need to add you to the author list!