Seen in the context of DAM tests at https://qa.nuxeo.org/jenkins/job/master/job/addons_FT_nuxeo-dam-master/org.nuxeo.marketplace.dam$webdriver/643/testReport/junit/org.nuxeo.ftest.cap/ITSearchTabTest(dam)/testSearch/
This error is triggered by a suggestion widget in the search form and produces the following stack trace server side:
This looks like a bad replacement of '?' characters in the query produced by the following page provider:
Strange thing is that seems to happen randomly...