Fixes checkTermExists bug 2

diff --git a/src/library/IndexDocumentBundle.php b/src/library/IndexDocumentBundle.php
index c22d888a4..2faed10e5 100644
--- a/src/library/IndexDocumentBundle.php
+++ b/src/library/IndexDocumentBundle.php
@@ -1148,7 +1148,7 @@ class IndexDocumentBundle implements CrawlConstants
      * @param string $terms_filter term bloom filter
      * @return boolean exists or not
      */
-    public function checkTermExists($term, $terms_filter)
+    public static function checkTermExists($term, $terms_filter)
     {
         $hash_functions = self::TERMSFILTER_HASHFN_COUNT;
         $size = self::TERMSFILTER_BITS_LEN;