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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 _ParseExtensionsString(self, extensions_string):
 """Parses the extensions string. Args: extensions_string (str):
 comma separated extensions to filter. """

    if not extensions_string:
      return

    extensions_string = extensions_string.lower()
    extensions = [
        extension.strip() for extension in extensions_string.split(',')]
    file_entry_filter = file_entry_filters.ExtensionsFileEntryFilter(extensions)
    self._filter_collection.AddFilter(file_entry_filter)