diff --git a/src/Primitive.php b/src/Primitive.php
index be695a9..2cba7c8 100644
--- a/src/Primitive.php
+++ b/src/Primitive.php
@@ -46,7 +46,7 @@ class Primitive {
     public static function to_date($value)
     {
         $result = 0;
-        $tmp = explode("/", $value, 3);
+        $tmp = explode("/", $value ?? '', 3);
         if (!empty($tmp)) {
             if (count($tmp) != 3) return $result;
 
diff --git a/src/Tools/StringUtil.php b/src/Tools/StringUtil.php
index 70c92e6..8fb208f 100644
--- a/src/Tools/StringUtil.php
+++ b/src/Tools/StringUtil.php
@@ -73,7 +73,7 @@ class StringUtil {
     }
 
     static function mb_str_split($str) {
-        return preg_split('~~u', $str, null, PREG_SPLIT_NO_EMPTY);
+        return preg_split('~~u', $str, -1, PREG_SPLIT_NO_EMPTY);
     }
 
     static function mb_strtr($str, $from, $to) {