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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 _get_mapping():
 """ Finds and loads gulp's rev-manifest.json file. In default, this is looking for rev-manifest.json file places in your STATIC_ROOT. Can be overriden to a specific location by setting DJANGO_GULP_REV_PATH. """

    global _STATIC_MAPPING

    if _STATIC_MAPPING is None:
        manifest_path = getattr(settings,
            'DJANGO_GULP_REV_PATH',
            os.path.join(getattr(settings, 'STATIC_ROOT', ''), 'rev-manifest.json'))
        
        try:
            with open(manifest_path) as manifest_file:
                _STATIC_MAPPING = json.load(manifest_file)
        except IOError:
            return None

    return _STATIC_MAPPING