Always return a string. Even if array was empty.

Author: vovayatsyuk

app/code/Magento/Customer/Model/Address/AbstractAddress.php

@@ -308,7 +308,11 @@ protected function _implodeArrayField(array $data)
      */
     protected function _implodeArrayValues($value)
     {
-        if (is_array($value) && count($value)) {
+        if (is_array($value)) {
+            if (!count($value)) {
+                return '';
+            }
+
             $isScalar = false;
             foreach ($value as $val) {
                 if (is_scalar($val)) {