Notice: Undefined index: base_path in base_path() (line 414

La La solución a este problema se encuentra acá
https://www.drupal.org/node/2782653#comment-11983873

diff --git a/flexslider.module b/flexslider.module
index ae04627..9bb02a2 100755
--- a/flexslider.module
+++ b/flexslider.module
@@ -8,9 +8,6 @@
 use Drupal\Core\Url;
 use Drupal\flexslider\Entity\Flexslider;
 
-define("FLEXSLIDER_VERSION", \Drupal::config('flexslider.settings')->get('flexslider_version'));
-define("FLEXSLIDER_DEBUG", \Drupal::config('flexslider.settings')->get('flexslider_debug'));
-
 /**
  * Implements hook_libraries_info().
  */
@@ -42,7 +39,7 @@ function flexslider_libraries_info() {
  * Implements hook_libraries_info_alter().
  */
 function flexslider_libraries_info_alter(&$libraries) {
-  $debug = FLEXSLIDER_DEBUG;
+  $debug = \Drupal::config('flexslider.settings')->get('flexslider_debug');
   if ($debug) {
     // Switch to the unminified version of the library.
     if (isset($libraries['flexslider'])) {
@@ -76,7 +73,8 @@ function flexslider_library_info_alter(&$libraries, $extension) {
     unset($libraries['flexslider']['css']['component']['flexslider.css']);
 
     // Enable debug mode.
-    if (FLEXSLIDER_DEBUG) {
+    $debug = \Drupal::config('flexslider.settings')->get('flexslider_debug');
+    if ($debug) {
       // Add the unminified version.
       $libraries['flexslider']['js'] = array(
         $library_path . '/jquery.flexslider.js' => array(),