Fix some user feedback form handling

sheesh i don't see how this hasn't been more broken for some time now...

tailbone/forms/core.py

@@ -923,6 +923,16 @@ class Form(object):
             # https://docs.pylonsproject.org/projects/pyramid/en/latest/api/request.html#pyramid.request.Request.is_xhr
             if self.request.is_xhr:
                 controls = self.request.json_body.items()
+
+                # TODO: why in the hell is this necessary?  some colander forms
+                # won't validate if a `None` sneaks its way through?  note, in
+                # particular this was needed to allow anonymous user feedback
+                controls = [[key, val] for key, val in controls]
+                for i in range(len(controls)):
+                    key, value = controls[i]
+                    if value is None:
+                        controls[i][1] = ''
+
             else:
                 controls = self.request.POST.items()