IF any of the arguments to ST_INTERSECTION is NULL for some reason, such as wrong WKT syntax, the server will assert as follows:

mysqld: item.cc:5907: virtual bool Item::send(Protocol*, String*): Assertion `!null_value' failed.

/lib/libc.so.6(__assert_fail+0xf8) [0x6b0d98]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(Item::send(Protocol*, String*)+0x91) [0x81db873]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(select_send::send_data(List<Item>&)+0x106) [0x8288f24]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(JOIN::exec()+0x3f4) [0x8325d74]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(mysql_select(THD*, Item**, TABLE_LIST, unsigned int, List<Item>&, Item*, unsigned int, st_order*, st_order*, Item*, st_order*, unsigned long long, select_result*, st_select_lex_unit*, st_select_lex*)+0x3c2) [0x8328790]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(handle_select(THD*, st_lex*, select_result*, unsigned long)+0x1cd) [0x832065b]
/home/philips/bzr/maria-5.3-gis/sql/mysqld() [0x82bbd8b]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(mysql_execute_command(THD*)+0x71e) [0x82b2b8f]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(mysql_parse(THD*, char*, unsigned int, char const**)+0x26f) [0x82be3c7]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(dispatch_command(enum_server_command, THD*, char*, unsigned int)+0x8e3) [0x82b082b]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(do_command(THD*)+0x27d) [0x82afcb1]
/home/philips/bzr/maria-5.3-gis/sql/mysqld(handle_one_connection+0x170) [0x82acd2c]

test case:

SELECT ST_INTERSECTION ( NULL , NULL ) ;

bzr version-info
revision-id: <email address hidden>
date: 2011-06-20 00:21:41 +0500
build-date: 2011-06-23 18:34:56 +0300
revno: 2982
branch-nick: maria-5.3-gis