<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_access_flags_string(self):
 """ Return the access flags string of the field :rtype: string """

        if self.access_flags_string == None:
            self.access_flags_string = get_access_flags_string(
                self.get_access_flags())

            if self.access_flags_string == "":
                self.access_flags_string = "0x%x" % self.get_access_flags()
        return self.access_flags_string