json Invalid JSON text: "Invalid encoding in string."

[raybon-lee]

public static function mysql_escape($fieldValue)
  {
      if (is_array($fieldValue)) {
          return array_map(__METHOD__, $fieldValue);
      }

      if (is_bool($fieldValue)) {
          return (int)$fieldValue;
      }

      if (self::is_json($fieldValue)) {
           return self::safeJson($fieldValue);
      }

      if (!empty($fieldValue) && is_string($fieldValue)) {
          return str_replace(
              ['\\', "\0", "\n", "\r", "'", '"', "\x1a"],
              ['\\\\', '\\0', '\\n', '\\r', "\\'", '\\"', '\\Z'],
              $fieldValue
          );
      }

      return $fieldValue;
  }

replace

 public static function mysql_escape($fieldValue)
    {
        if (is_array($fieldValue)) {
            return array_map(__METHOD__, $fieldValue);
        }

        if (is_bool($fieldValue)) {
            return (int)$fieldValue;
        }

        if (self::is_json($fieldValue)) {
             fieldValue = self::safeJson($fieldValue);
        }

        if (!empty($fieldValue) && is_string($fieldValue)) {
            return str_replace(
                ['\\', "\0", "\n", "\r", "'", '"', "\x1a"],
                ['\\\\', '\\0', '\\n', '\\r', "\\'", '\\"', '\\Z'],
                $fieldValue
            );
        }

        return $fieldValue;
    }

note: The Json field may contain special characters of mysql, which should be handled again, not just the string type