CODE EXAMPLE FOR DART

map of a map in flutter

Map someThing = {
    "someThing2":{
      'key1': 'val1',
      'key2': 'val2',
      'key3': {},
    }
  };
// {someThing2: {key1: val1, key2: val2, key3: {}}}
someThing['someThing2']['key3'] = {
    'someThing3': {
          'key4': 'val4',
        },
  };
// {someThing2: {key1: val1, key2: val2, key3: {someThing3: {key4: val4}}}}