The `SELECT col FROM t WHERE col NOT IN (col, ...) GROUP BY col'
crashed in the range optimizer.

The get_func_mm_tree function has been modified to check the
Item_func_in::array field for the NULL value before using of that
value.


sql/opt_range.cc:
  Fixed bug #31075.
  The get_func_mm_tree function has been modified to check the
  Item_func_in::array field for the NULL value before using of that
  value.
mysql-test/t/func_in.test:
  Added test case for bug #31075.
mysql-test/r/func_in.result:
  Added test case for bug #31075.