change variable name

lms/static/js/spec/student_account/account_settings_fields_spec.js

@@ -55,7 +55,7 @@ define(['backbone',
                     groupOptions: [{
                         groupTitle: gettext('All Time Zones'),
                         selectOptions: FieldViewsSpecHelpers.SELECT_OPTIONS,
-                        blankTitle: 'Default (Local Time Zone)'
+                        nullValueOptionLabel: 'Default (Local Time Zone)'
                     }],
                     persistChanges: true,
                     required: true

lms/static/js/student_account/views/account_settings_factory.js

@@ -119,7 +119,7 @@
                                 groupOptions: [{
                                     groupTitle: gettext('All Time Zones'),
                                     selectOptions: fieldsData.time_zone.options,
-                                    blankTitle: gettext('Default (Local Time Zone)')
+                                    nullValueOptionLabel: gettext('Default (Local Time Zone)')
                                 }],
                                 persistChanges: true
                             })

lms/templates/fields/field_dropdown_account.underscore

@@ -22,8 +22,8 @@
         <select name="select" id="u-field-select-<%- id %>" aria-describedby="u-field-help-message-<%- id %>">
             <% _.each(groupOptions, function(groupOption) { %>
                 <% if (showBlankOption) { %>
-                    <% if (groupOption.blankTitle) { %>
-                        <option value=""><%- groupOption.blankTitle %></option>
+                    <% if (groupOption.nullValueOptionLabel) { %>
+                        <option value=""><%- groupOption.nullValueOptionLabel %></option>
                     <% } else { %>
                         <option value=""></option>
                     <% } %>