Returns the EmptyVal instance for the given type

def placeholder(type_):
    """Returns the EmptyVal instance for the given type"""
    typetuple = type_ if isinstance(type_, tuple) else (type_,)
    if any in typetuple:
        typetuple = any
    if typetuple not in EMPTY_VALS:
        EMPTY_VALS[typetuple] = EmptyVal(typetuple)
    return EMPTY_VALS[typetuple]