Notice on indexation with SolR 3.1

I've got a PHP notice on the index function with SolR 3.1 :

PHP Notice :
Notice: Undefined variable: expectedLength in /.../Search/src/handlers/solr.php on line 305

Stack trace :
...
21 5.5022 21616964 ezcSearchSolrHandler->index( ) ../search_session.php:151
22 5.5051 21618372 ezcSearchSolrHandler->sendRawPostCommand( ) ../solr.php:897