Illegal string offset 'value' processor.inc:336

I ran into an issue when running drush sapi-i . So when I am indexing, I noticed these message(s) (using PHP7.1) :

• "Illegal string offset 'value' processor.inc:331"

it happens in :

  protected function implodeTokens(array $tokens) {
    $ret = array();
    foreach ($tokens as $token) {
      if (empty($token['value']) && !is_numeric($token['value'])) {
        // Filter out empty tokens.
        continue;
      }
      if (is_array($token['value'])) {
        $ret[] = $this->implodeTokens($token['value']);
      }
      else {
        $ret[] = $token['value'];
      }
    }
    return implode(' ', $ret);
  }

Sometimes the token just consists out of numbers/id's , example :

array(5) {
  [0]=>
  string(4) "1485"
  [1]=>
  string(4) "1599"
  [2]=>
  string(4) "1501"
  [3]=>
  string(4) "1503"
  [4]=>
  string(4) "1481"
}

so I have added an extra check to only process when the key 'value' exists.