<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def custom_licenses(self):
 """Returns a string of the installed licenses the J-Link has. Args: self (JLink):
 the ``JLink`` instance Returns: String of the contents of the custom licenses the J-Link has. """

        buf = (ctypes.c_char * self.MAX_BUF_SIZE)()
        result = self._dll.JLINK_EMU_GetLicenses(buf, self.MAX_BUF_SIZE)
        if result < 0:
            raise errors.JLinkException(result)
        return ctypes.string_at(buf).decode()