In the VisualEditor, click the ≡ icon, click "Options", and choose "Page Settings".
If someone puts an invalid page name / page title in the "Target page for redirection" field (like the page name "Talk:" or a page name with a pipe character | in it), and tries to apply the changes, an exception is caused and the editor is locked up.
The "Apply Changes" button should be disabled when the input is not valid (like in e.g. the "Insert ➙ Media" dialog when file dimensions are invalid).
You are expected to provide a patch in Wikimedia Gerrit. See https://www.mediawiki.org/wiki/Gerrit/Tutorial for how to set up Git and Gerrit.