Toggling Template editor off of Freemarker language throws UI error

• Type: Regression Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.0.0 M6
• Fix Version/s: 7.0.0 M6
• Component/s: Dynamic Data Mapping, Dynamic Data Mapping > Template Editor, WCM > Application Display Templates
• Labels: None
• Fix Priority: 4
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/27317

Steps to reproduce:

1. Navigate to Admin > Content > Web Content > Manage > Templates
2. Begin to add a Template
   • In the Detalis dropdown, toggle the language to Velocity (.vm) or XSL

Expected result:
User will be able to write the Velocity template.

Actual result:
Toggling to Velocity language navigates back to the Templates list, and throws a "Your request failed to complete." UI error message. See attached gif.