FormBuilder(
  child: Column(
    mainAxisAlignment: MainAxisAlignment.center,
    children: <Widget>[
      FormBuilderImagePicker(
        name: 'photos',
        decoration: const InputDecoration(labelText: 'Pick Photos'),
        maxImages: 1,
      ),
      const SizedBox(height: 15),
      RaisedButton(onPressed: (){
        if(_formKey.currentState.saveAndValidate()){
          print(_formKey.currentState.value);
        }
      })
    ],
  ),
),