Function 'in' of class Expr does not work with an array of strings as parameter

Function in of Expr seems not to work properly.
I tried to fetch a result using a query with the function in() of Expr as described in the doctirne 2.0 documentation (querying an object Offer that contains a column named 'state' of type string)):

$qb->select('ofr')
->from('Offer', 'ofr')
>where($qb>expr()->in('ofr.state', array('test','second value','third value')));
$query = $qb->getQuery();
$result = $query->getResult();

Then the following error occurs:
[Syntax Error] line 0, col 139: Error: Expected Literal, got 'test'
in ...Doctrine/ORM/Query/QueryException.php, on line 41

Stack:
Doctrine\ORM\Query\QueryException::syntaxError( string ) in ...Doctrine/ORM/Query/Parser.php on line 346
Doctrine\ORM\Query\Parser->syntaxError( string ) in ...Doctrine/ORM/Query/Parser.php on line 2032
Doctrine\ORM\Query\Parser->Literal( ) in ...Doctrine/ORM/Query/Parser.php on line 2047
Doctrine\ORM\Query\Parser->InParameter( ) in ...Doctrine/ORM/Query/Parser.php on line 2423
Doctrine\ORM\Query\Parser->InExpression( ) in ...Doctrine/ORM/Query/Parser.php on line 1928
Doctrine\ORM\Query\Parser->SimpleConditionalExpression( ) in ...Doctrine/ORM/Query/Parser.php on line 1858
Doctrine\ORM\Query\Parser->ConditionalPrimary( ) in ...Doctrine/ORM/Query/Parser.php on line 1815
Doctrine\ORM\Query\Parser->ConditionalFactor( ) in ...Doctrine/ORM/Query/Parser.php on line 1791
Doctrine\ORM\Query\Parser->ConditionalTerm( ) in ...Doctrine/ORM/Query/Parser.php on line 1773
Doctrine\ORM\Query\Parser->ConditionalExpression( ) in ...Doctrine/ORM/Query/Parser.php on line 1854
Doctrine\ORM\Query\Parser->ConditionalPrimary( ) in ...Doctrine/ORM/Query/Parser.php on line 1815
Doctrine\ORM\Query\Parser->ConditionalFactor( ) in ...Doctrine/ORM/Query/Parser.php on line 1795
Doctrine\ORM\Query\Parser->ConditionalTerm( ) in ...Doctrine/ORM/Query/Parser.php on line 1773
Doctrine\ORM\Query\Parser->ConditionalExpression( ) in ...Doctrine/ORM/Query/Parser.php on line 1273
Doctrine\ORM\Query\Parser->WhereClause( ) in ...Doctrine/ORM/Query/Parser.php on line 810
Doctrine\ORM\Query\Parser->SelectStatement( ) in ...Doctrine/ORM/Query/Parser.php on line 780
Doctrine\ORM\Query\Parser->QueryLanguage( ) in ...Doctrine/ORM/Query/Parser.php on line 275
Doctrine\ORM\Query\Parser->parse( ) in ...Doctrine/ORM/Query.php on line 159
Doctrine\ORM\Query->_parse( ) in ...Doctrine/ORM/Query.php on line 193
Doctrine\ORM\Query->_doExecute( array ) in ...Doctrine/ORM/AbstractQuery.php on line 511
Doctrine\ORM\AbstractQuery->execute( array, integer ) in ...Doctrine/ORM/AbstractQuery.php on line 349
Doctrine\ORM\AbstractQuery->getResult( )