docs: def get_value(self, name, parameters=None):
          """Return the value of a cached variable if applicable
  
          The value of the variable 'name' is returned, if no parameters are passed or if all parameters are identical
          to the ones stored for the variable.
  
          :param str name: Name of teh variable
          :param dict parameters: Current parameters or None if parameters do not matter
          :return: The cached value of the variable or None if the parameters differ
          """
          if not isinstance(parameters, dict):
              raise TypeError("parameters must a dict")
          if name not in self._cache:
              return None
          hash = self._parameter_hash(parameters)
          hashdigest = hash.hexdigest()
          return self._cache[name].get(hashdigest, None)