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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 add_namespace(self, namespace):
 """ Add a CIM namespace to the mock repository. The namespace must not yet exist in the mock repository. Note that the default connection namespace is automatically added to the mock repository upon creation of this object. Parameters: namespace (:term:`string`):
 The name of the CIM namespace in the mock repository. Must not be `None`. Any leading and trailing slash characters are split off from the provided string. Raises: ValueError: Namespace argument must not be None CIMError: CIM_ERR_ALREADY_EXISTS if the namespace already exists in the mock repository. """


        if namespace is None:
            raise ValueError("Namespace argument must not be None")

        # Normalize the namespace name
        namespace = namespace.strip('/')

        if namespace in self.namespaces:
            raise CIMError(
                CIM_ERR_ALREADY_EXISTS,
                _format("Namespace {0!A} already exists in the mock "
                        "repository", namespace))

        self.namespaces[namespace] = True