BUG#18752: Also handle NULL values in VALUES LESS THAN

mysql-test/r/partition.result:
  Added test case to verify that VALUES LESS THAN (NULL) isn't allowed
mysql-test/t/partition.test:
  Added test case to verify that VALUES LESS THAN (NULL) isn't allowed
sql/share/errmsg.txt:
  Added new error message
sql/sql_yacc.yy:
  Added error check for null value

mysql-test/r/partition.result

@@ -848,4 +848,8 @@ t1	CREATE TABLE `t1` (
   `a` int(11) DEFAULT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 PARTITION BY LIST (a) (PARTITION p0 VALUES IN (NULL) ENGINE = MyISAM)
 DROP TABLE t1;
+CREATE TABLE t1 (a int)
+PARTITION BY RANGE(a)
+(PARTITION p0 VALUES LESS THAN (NULL));
+ERROR 42000: Not allowed to use NULL value in VALUES LESS THAN near '))' at line 3
 End of 5.1 tests

mysql-test/t/partition.test

@@ -965,4 +965,9 @@ PARTITION BY LIST (a)
 SHOW CREATE TABLE t1;
 DROP TABLE t1;
 
+--error 1064
+CREATE TABLE t1 (a int)
+PARTITION BY RANGE(a)
+(PARTITION p0 VALUES LESS THAN (NULL));
+
 --echo End of 5.1 tests

sql/share/errmsg.txt

@@ -5826,3 +5826,6 @@ ER_NDB_CANT_SWITCH_BINLOG_FORMAT
 	eng "The NDB cluster engine does not support changing the binlog format on the fly yet"
 ER_PARTITION_NO_TEMPORARY
 	eng "Cannot create temporary table with partitions"
+ER_NULL_IN_VALUES_LESS_THAN
+        eng "Not allowed to use NULL value in VALUES LESS THAN"
+        swe "Det är inte tillåtet att använda NULL-värden i VALUES LESS THAN"

sql/sql_yacc.yy

@@ -3721,6 +3721,11 @@ part_func_max:
             yyerror(ER(ER_PARTITION_MAXVALUE_ERROR));
             YYABORT;
           }
+          if (Lex->part_info->curr_part_elem->has_null_value)
+          {
+            yyerror(ER(ER_NULL_IN_VALUES_LESS_THAN));
+            YYABORT;
+          }
         }
         ;