Resolve "not checked `referred by` checkbox causes error"

Closes #468 (closed)

smash/web/templates/subjects/add.html

@@ -102,13 +102,18 @@
     <script src="{% static 'npm/awesomplete/awesomplete.min.js' %}"></script>
     <script>
         $(document).ready(function () {
-
-            var cityInput = document.querySelector("#id_subject-city");
             var referralInput = document.querySelector("#id_study_subject-referral");
+            if (referralInput !== null) {
+                $.get("{% url 'web.api.referrals' %}", function (data) {
+                    new Awesomplete(referralInput).list = data.referrals;
+                });
+            }
+            
+            var cityInput = document.querySelector("#id_subject-city");
             var lastNameInput = $("input[name='subject-last_name']");
             var firstNameInput = $("input[name='subject-first_name']");
 
-            if (cityInput === null || referralInput === null || lastNameInput.length === 0 || firstNameInput.length === 0) {
+            if (cityInput === null || lastNameInput.length === 0 || firstNameInput.length === 0) {
                 alert("Internal error. Contact administrators.");
             }
 
@@ -116,9 +121,6 @@
             $.get("{% url 'web.api.cities' %}", function (data) {
                 new Awesomplete(cityInput).list = data.cities;
             });
-            $.get("{% url 'web.api.referrals' %}", function (data) {
-                new Awesomplete(referralInput).list = data.referrals;
-            });
 
 
             var checkDuplicates = function (e) {