Issue Collector Error Message is not shown without changing the Issue Type

Steps to reproduce:

1. Go to General Configuration and set Allow unassigned issues setting to Off. The Assignee field will be automatically set to Required in the Field Configuration.
2. Create a new project and make the Project Lead as the Default Assignee
3. Go to Project Administration -> Issue Collectors -> Add Issue Collector
4. Key in all the required field and click Submit

Current Result:

• The page is refreshed and returns to the same page without any error message shown until the users change the Issue Type

Expected Result:

• The error message should be displayed without changing the Issue Type

  Error
  
  You cannot create an issue collector for this project, because the following fields are required on the project and those field types cannot be displayed to anonymous users. If the field is changed to be optional or a default value is provided, then an Issue Collector can be created for the project. Not allowed fields: Assignee
  

Workaround:

• Set Allow unassigned issues setting to On in General Configuration

Note:
This can also be reproduced by setting a field type that is not allowed in Issue Collector as required, for example a user picker field.