make rpc_groups attribute optional

@register.filter(name="rpc_groups_from_function")

def rpc_groups_from_function(fn_name: str) -> str:

    fn = all_methods[fn_name]

    return " ".join(fn.rpc_groups)

    return " ".join(getattr(fn, "rpc_groups", []))

@register.filter(name="rpc_groups_as_list")

def rpc_groups_as_list(fns) -> list:

    groups = []

    for _, fn in fns:

        for group in fn.rpc_groups:

        grps = getattr(fn, "rpc_groups", [])

        for group in grps:

            groups.append(group)

    return list(set(groups))