docs: def clear_breakpoint(self, breakpoint_number):
          """ Delete a breakpoint identified by it's number. 
          
          :param breakpoint_number:  index of breakpoint to delete
          :type breakpoint_number: int
          :return: an error message or None
          """
          if not (0 <= breakpoint_number < len(IKBreakpoint.breakpoints_by_number)):
              return "Found no breakpoint numbered %s" % breakpoint_number
          bp = IKBreakpoint.breakpoints_by_number[breakpoint_number]
          if not bp:
              return "Found no breakpoint numbered: %s" % breakpoint_number
          _logger.b_debug("    clear_breakpoint(breakpoint_number=%s) found: %s",
                          breakpoint_number,
                          bp)
          bp.clear()
          if self.pending_stop or IKBreakpoint.any_active_breakpoint:
              self.enable_tracing()
          else:
              self.disable_tracing()
          return None