Description:
------------
I've used the php_solr.dll file from windows.php.net, which is version 0.9.7.

When doing getResponse() on the SolrQueryResponse object PHP seems to crash when it contains an empty field.

When var_dump'ing the query response the empty field looks like:
<str name="s_full_description"/>

When filling the field, the problem doesn't occur, so the response contains this:
<str name="s_full_description">something</str>

Reproduce code:
---------------
// make sure there's a field with no data
$document->addField('s_short_description', '');

// retrieve the field
$options = array( ... );
$client = new SolrClient($options);
$query = new SolrQuery();
$results = $query->setQuery('*:*');
$query->setStart(0);
$query->setRows(10);
$query->addField('id');
$query->addField('s_full_description'); // when leaving this out, it works correctly
$queryResponse = $client->query($query);
$response = $queryResponse->getResponse(); // makes it crash

Expected result:
----------------
not to crash

Actual result:
--------------
php stopped working