test case added for the bug #31155

mysql-test/r/gis.result:
  test result complete
mysql-test/t/gis.test:
  test case added for the bug

mysql-test/r/gis.result

@@ -957,4 +957,10 @@ COUNT(*)
 2
 DROP TABLE t1, t2;
 End of 5.0 tests
+create table `t1` (`col002` point)engine=myisam;
+insert into t1 values (),(),();
+select min(`col002`) from t1 union select `col002` from t1;
+min(`col002`)
+NULL
+drop table t1;
 End of 5.0 tests

mysql-test/t/gis.test

@@ -631,4 +631,13 @@ SELECT 1;
 
 -- source include/gis_keys.inc
 
+#
+# Bug #31155 gis types in union'd select cause crash
+#
+
+create table `t1` (`col002` point)engine=myisam;
+insert into t1 values (),(),();
+select min(`col002`) from t1 union select `col002` from t1;
+drop table t1;
+
 --echo End of 5.0 tests