Server error when editing a page without approvers when a minimum number is requested

Reproduction steps:

• Create a page
• Enable minimum number of explicit approvers and set it to 2
• Edit the created page and save as change request
• Put 2 approvers in the modal
• Save

Expected result:

• the page is properly saved in a CR with 2 approvers

Obtained result:

• we obtain an error 500 with:

  Caused by: 
  org.xwiki.contrib.changerequest.ChangeRequestException: The minimum number of approvers [2] has not been respected: only [0] approvers defined.
  	at org.xwiki.contrib.changerequest.internal.handlers.AbstractChangeRequestActionHandler.copyApprovers(AbstractChangeRequestActionHandler.java:299)
  	at org.xwiki.contrib.changerequest.internal.handlers.CreateChangeRequestHandler.handle(CreateChangeRequestHandler.java:91)
  	at org.xwiki.contrib.changerequest.internal.handlers.ChangeRequestResourceHandler.handle(ChangeRequestResourceHandler.java:139)
  	at org.xwiki.resource.internal.DefaultResourceReferenceHandlerChain.handleNext(DefaultResourceReferenceHandlerChain.java:79)
  	at org.xwiki.resource.internal.AbstractResourceReferenceHandlerManager.handle(AbstractResourceReferenceHandlerManager.java:82)
  	at org.xwiki.resource.servlet.ResourceReferenceHandlerServlet.handleResourceReference(ResourceReferenceHandlerServlet.java:159)
  	at org.xwiki.resource.servlet.ResourceReferenceHandlerServlet.service(ResourceReferenceHandlerServlet.java:87)
  

Apparently the root cause is that the JS doesn't inject the values for the approvers in case of edition.