diff --git a/CRM/Twingle/Form/Profile.php b/CRM/Twingle/Form/Profile.php
index 59dee93..e0dcca8 100644
--- a/CRM/Twingle/Form/Profile.php
+++ b/CRM/Twingle/Form/Profile.php
@@ -364,58 +364,60 @@ class CRM_Twingle_Form_Profile extends CRM_Core_Form {
 
     // Validate custom field mapping.
     try {
-      $custom_field_mapping = preg_split('/\r\n|\r|\n/', $values['custom_field_mapping'], -1, PREG_SPLIT_NO_EMPTY);
-      if (!is_array($custom_field_mapping)) {
-        throw new Exception(
-          E::ts('Could not parse custom field mapping.')
-        );
-      }
-      foreach ($custom_field_mapping as $custom_field_map) {
-        $custom_field_map = explode("=", $custom_field_map);
-        if (count($custom_field_map) !== 2) {
+      if (isset($values['custom_field_mapping'])) {
+        $custom_field_mapping = preg_split('/\r\n|\r|\n/', $values['custom_field_mapping'], -1, PREG_SPLIT_NO_EMPTY);
+        if (!is_array($custom_field_mapping)) {
           throw new Exception(
             E::ts('Could not parse custom field mapping.')
           );
         }
-        list($twingle_field_name, $custom_field_name) = $custom_field_map;
-        $custom_field_id = substr($custom_field_name, strlen('custom_'));
+        foreach ($custom_field_mapping as $custom_field_map) {
+          $custom_field_map = explode("=", $custom_field_map);
+          if (count($custom_field_map) !== 2) {
+            throw new Exception(
+              E::ts('Could not parse custom field mapping.')
+            );
+          }
+          list($twingle_field_name, $custom_field_name) = $custom_field_map;
+          $custom_field_id = substr($custom_field_name, strlen('custom_'));
 
-        // Check for custom field existence
-        try {
-          $custom_field = civicrm_api3('CustomField', 'getsingle', array(
-            'id' => $custom_field_id,
-          ));
-        }
-        catch (CiviCRM_API3_Exception $exception) {
-          throw new Exception(
-            E::ts(
-              'Custom field custom_%1 does not exist.',
-              array(1 => $custom_field_id)
-            )
-          );
-        }
+          // Check for custom field existence
+          try {
+            $custom_field = civicrm_api3('CustomField', 'getsingle', array(
+              'id' => $custom_field_id,
+            ));
+          }
+          catch (CiviCRM_API3_Exception $exception) {
+            throw new Exception(
+              E::ts(
+                'Custom field custom_%1 does not exist.',
+                array(1 => $custom_field_id)
+              )
+            );
+          }
 
-        // Only allow custom fields on relevant entities.
-        try {
-          $custom_group = civicrm_api3('CustomGroup', 'getsingle', array(
-            'id' => $custom_field['custom_group_id'],
-            'extends' => array(
-              'IN' => array(
-                'Contact',
-                'Individual',
-                'Organization',
-                'Contribution',
-                'ContributionRecur',
+          // Only allow custom fields on relevant entities.
+          try {
+            $custom_group = civicrm_api3('CustomGroup', 'getsingle', array(
+              'id' => $custom_field['custom_group_id'],
+              'extends' => array(
+                'IN' => array(
+                  'Contact',
+                  'Individual',
+                  'Organization',
+                  'Contribution',
+                  'ContributionRecur',
+                ),
               ),
-            ),
-          ));
-        } catch (CiviCRM_API3_Exception $exception) {
-          throw new Exception(
-            E::ts(
-              'Custom field custom_%1 is not in a CustomGroup that extends one of the supported CiviCRM entities.',
-              array(1 => $custom_field['id'])
-            )
-          );
+            ));
+          } catch (CiviCRM_API3_Exception $exception) {
+            throw new Exception(
+              E::ts(
+                'Custom field custom_%1 is not in a CustomGroup that extends one of the supported CiviCRM entities.',
+                array(1 => $custom_field['id'])
+              )
+            );
+          }
         }
       }
     }