The following exception appears in the logs while hitting the following API URL.
2018-01-02 20:52:24 [WkvxCApAEDUAAFS2uOwAAAAW] mw1288 wikidatawiki 1.31.0-wmf.12 exception ERROR: [WkvxCApAEDUAAFS2uOwAAAAW] /w/api.php?action=wbcheckconstraints&format=json&formatversion=2&uselang=en&id=Q1433459 WikibaseQuality\ConstraintReport\ConstraintCheck\Helper\ConstraintParameterException from line 454 of /srv/mediawiki/php-1.31.0-wmf.12/extensions/WikibaseQualityConstraints/includes/ConstraintCheck/Helper/SparqlHelper.php: <span class="wbqc-role wbqc-role-constraint-parameter-value"><code><nowiki>[^{}[\]<>:]+</nowiki></code></span> is not a valid regular expression. {"exception_id":"WkvxCApAEDUAAFS2uOwAAAAW","exception_url":"/w/api.php?action=wbcheckconstraints&format=json&formatversion=2&uselang=en&id=Q1433459","caught_by":"mwe_handler"} [Exception WikibaseQuality\ConstraintReport\ConstraintCheck\Helper\ConstraintParameterException] (/srv/mediawiki/php-1.31.0-wmf.12/extensions/WikibaseQualityConstraints/includes/ConstraintCheck/Helper/SparqlHelper.php:454) <span class="wbqc-role wbqc-role-constraint-parameter-value"><code><nowiki>[^{}[\]<>:]+</nowiki></code></span> is not a valid regular expression. #0 /srv/mediawiki/php-1.31.0-wmf.12/extensions/WikibaseQualityConstraints/includes/ConstraintCheck/Helper/SparqlHelper.php(395): WikibaseQuality\ConstraintReport\ConstraintCheck\Helper\SparqlHelper->matchesRegularExpressionWithSparql(string, string) #1 /srv/mediawiki/php-1.31.0-wmf.12/includes/libs/objectcache/WANObjectCache.php(1168): Closure$WikibaseQuality\ConstraintReport\ConstraintCheck\Helper\SparqlHelper::matchesRegularExpression(array, integer, array, double) #2 /srv/mediawiki/php-1.31.0-wmf.12/includes/libs/objectcache/WANObjectCache.php(1107): WANObjectCache->doGetWithSetCallback(string, integer, Closure$WikibaseQuality\ConstraintReport\ConstraintCheck\Helper\SparqlHelper::matchesRegularExpression;1141, array, double) #3 /srv/mediawiki/php-1.31.0-wmf.12/includes/deferred/MWCallableUpdate.php(30): Closure$WANObjectCache::doGetWithSetCallback() #4 /srv/mediawiki/php-1.31.0-wmf.12/includes/deferred/DeferredUpdates.php(259): MWCallableUpdate->doUpdate() #5 /srv/mediawiki/php-1.31.0-wmf.12/includes/deferred/DeferredUpdates.php(210): DeferredUpdates::runUpdate(MWCallableUpdate, Wikimedia\Rdbms\LBFactoryMulti, string, integer) #6 /srv/mediawiki/php-1.31.0-wmf.12/includes/deferred/DeferredUpdates.php(131): DeferredUpdates::execute(array, string, integer) #7 /srv/mediawiki/php-1.31.0-wmf.12/includes/MediaWiki.php(897): DeferredUpdates::doUpdates(string) #8 /srv/mediawiki/php-1.31.0-wmf.12/includes/MediaWiki.php(719): MediaWiki->restInPeace(string, boolean) #9 [internal function]: Closure$MediaWiki::doPostOutputShutdown() #10 {main}