ModelContextTag does not properly clear the model when set to null

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.1.0 CE GA1, 6.1.10 EE GA1, 6.2.0 CE M2
• Fix Version/s: 6.1.1 CE GA2, 6.1.20 EE GA2, --Sprint 11/12, 6.2.0 CE M2
• Component/s: ~ [Archived] Frontend Infrastructure
• Labels: None
• Branch Version/s:
  6.1.x
• Backported to Branch:
  Committed
• Liferay Contributor's Agreement:
  Accept
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/5353

when you set the model attribute of a ModelContextTag to null like this

<aui:model-context model="<%= null %>" />

then the aui:model-context:model pageContext attribute is not removed as it should be