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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _validate_storage(storage, service_name, add_error):
 """Lazily validate the storage constraints, ensuring that they are a dict. Use the given add_error callable to register validation error. """

    if storage is None:
        return
    if not isdict(storage):
        msg = 'service {} has invalid storage constraints {}'.format(
            service_name, storage)
        add_error(msg)