@validator('mapping')
def backwards_compatibility(cls, mapping: Mapping[(str, str)]):
    return {key.replace('.$[', '['): value.replace('.$[', '[') for (key, value) in mapping.items()}
@validator('mapping')
def backwards_compatibility(cls, mapping: Mapping[(str, str)]):
    return {key.replace('.$[', '['): value.replace('.$[', '[') for (key, value) in mapping.items()}