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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 replace_pyof_version(module_fullname, version):
 """Replace the OF Version of a module fullname. Get's a module name (eg. 'pyof.v0x01.common.header') and returns it on a new 'version' (eg. 'pyof.v0x02.common.header'). Args: module_fullname (str):
 The fullname of the module (e.g.: pyof.v0x01.common.header) version (str):
 The version to be 'inserted' on the module fullname. Returns: str: module fullname The new module fullname, with the replaced version, on the format "pyof.v0x01.common.header". If the requested version is the same as the one of the module_fullname or if the module_fullname is not a 'OF version' specific module, returns None. """

        module_version = MetaStruct.get_pyof_version(module_fullname)
        if not module_version or module_version == version:
            return None

        return module_fullname.replace(module_version, version)