Now all modules are in core modules folder

modules/content_taxonomy/includes/views/content_taxonomy.views.inc

@@ -0,0 +1,17 @@
+<?php
+
+/**
+ * Implementation of hook_views_handlers().
+ */
+function content_taxonomy_views_handlers() {
+  return array(
+    'info' => array(
+      'path' => drupal_get_path('module', 'content_taxonomy') . '/includes/views',
+    ),
+    'handlers' => array(
+      'content_taxonomy_handler_filter_many_to_one' => array(
+        'parent' => 'content_handler_filter_many_to_one',
+      ),
+    ),
+  );
+}

modules/content_taxonomy/includes/views/content_taxonomy_handler_filter_many_to_one.inc

@@ -0,0 +1,21 @@
+<?php
+
+/**
+ * Subclass of views_handler_filter_many_to_one_content
+ *
+ * provides values for the filters
+ * unsets the empty value for non required fields, which is added content_taxonomy_allowed_values
+ */
+class content_taxonomy_handler_filter_many_to_one extends content_handler_filter_many_to_one {
+  var $content_field;
+
+  function construct() {
+    parent::construct();
+  }
+
+  function get_value_options() {
+    $options = content_taxonomy_allowed_values($this->content_field);
+    unset($options['']);
+    $this->value_options = $options;
+  }
+}