Create an instance from a dictionary.

def from_dict(cls, d):
        """
        Create an instance from a dictionary.
        """
        execution_request = super(ExecutionRequest, cls).from_dict(d)
        if isinstance(execution_request.simulation_group, dict):
            execution_request.simulation_group = SimulationGroup.from_dict(execution_request.simulation_group)
        return execution_request