code: def add(self, variables: Dict[str, str], overwrite: bool=False):
          
          preset_variables = self._project.variables.list()
          preset_variable_keys = [variable.key for variable in preset_variables]
  
          for key, value in variables.items():
              if key in preset_variable_keys:
                  if overwrite:
                      variable = preset_variables[preset_variable_keys.index(key)]
                      variable.value = value
                      variable.save()
              else:
                  variable = self._project.variables.create({
                      _VARIABLE_KEY_PROPERTY: key, _VARIABLE_VALUE_PROPERTY: value})
                  variable.save()
docs: Adds the given build variables to those that already exist.
          :param variables: the build variables to add
          :param overwrite: whether the old variable should be overwritten in the case of a redefinition