project_submission: handle case of an unassigned project.

On the submission page we display a contact address for the project
editor, if one has been assigned.  If no editor has yet been assigned,
then the "contact_email" won't be shown.

However, if no editor has yet been assigned (self.editor is None) and
there is no PROJECT_EDITOR_EMAIL defined, the previous code would
crash.

Put this logic into the model class, not the view, and document it.

physionet-django/project/modelcomponents/unpublishedproject.py

@@ -103,6 +103,29 @@ def has_wfdb(self):
         """
         return self.files.has_wfdb_files(self)
 
+    @property
+    def editor_contact_email(self):
+        """
+        Email address for contacting the project editor.
+
+        If a site-wide contact address is configured, that address
+        will be used for all projects.  The string PROJECT-SLUG can be
+        included and will be replaced by the active project slug (for
+        example, PROJECT_EDITOR_EMAIL can be set to
+        '[email protected]', if the mail server
+        understands how to handle it.)
+
+        If there is no site-wide contact address, the primary email
+        address of the assigned editor is used.
+        """
+        if not self.editor:
+            return None
+        elif settings.PROJECT_EDITOR_EMAIL:
+            return settings.PROJECT_EDITOR_EMAIL.replace('PROJECT-SLUG',
+                                                         self.slug)
+        else:
+            return self.editor.email
+
     def content_modified(self):
         """
         Update the project's modification timestamp.

physionet-django/project/views.py

@@ -1418,12 +1418,6 @@ def project_submission(request, project_slug, **kwargs):
     else:
         edit_logs, copyedit_logs = None, None
 
-    if settings.PROJECT_EDITOR_EMAIL:
-        contact_email = settings.PROJECT_EDITOR_EMAIL.replace('PROJECT-SLUG',
-                                                              project.slug)
-    else:
-        contact_email = project.editor.email
-
     return render(
         request,
         "project/project_submission.html",
@@ -1435,7 +1429,7 @@ def project_submission(request, project_slug, **kwargs):
             "edit_logs": edit_logs,
             "copyedit_logs": copyedit_logs,
             "awaiting_user_approval": awaiting_user_approval,
-            "contact_email": contact_email,
+            "contact_email": project.editor_contact_email,
         },
     )