I recently tried to enable $sfgCacheFormDefinitions and $sfgFormCacheType to speed up forms:

$sfgCacheFormDefinitions = true;
$sfgFormCacheType = CACHE_ANYTHING;

After enabling trying to edit with this form:

http://wikiapiary.com/w/index.php?title=WikiApiary&action=formedit

Started throwing an exception (full message here, paths truncated):

2013/06/26 09:01:44 [error] 13514#0: *3293810 FastCGI sent in stderr: "PHP message: PHP Notice: Trying to get property of non-object in .../extensions/Variables/Variables.php on line 208
PHP message: PHP Catchable fatal error: Argument 2 passed to SMW\ParserData::__construct() must be an instance of ParserOutput, null given, called in .../extensions/SemanticMediaWiki/SemanticMediaWiki.hooks.php on line 688 and defined in .../extensions/SemanticMediaWiki/includes/ParserData.php on line 177" while reading response header from upstream, client: 173.165.236.113, server: wikiapiary.com, request: "GET /w/index.php?title=WikiApiary&action=formedit HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "wikiapiary.com", referrer: "http://wikiapiary.com/wiki/WikiApiary"

None of those errors are in Semantic Forms code, but the error seems to be caused by these settings.

Note that if I resaved Form:Website and then did Edit with Form, it would work on the first request. All subsequent requests then generated the exception.

Also, this error was true for all forms on the site, not just this one example.

Version: master
Severity: normal