"GET /%7Bnull%7D HTTP/1.1" 404 error

After we dynamically upgrade SmartGWT to a new version, the table grid becomes empty. There are errors in Jetty request.log:
"GET /%7Bnull%7D HTTP/1.1" 404

What is the file we try to retrieve?

Meanwhile, there are errors in the Jetty log file:
com.google.gwt.core.client.JavaScriptException: (TypeError)
description: Unable to set property 'innerHTML' of undefined or null reference
number: -2146823281: Unable to set property 'innerHTML' of undefined or null reference