I got this error if I searched in the admin interface.

The problem is in method classIdentifier of ezcontentobjecttreenode:

 5421;           $object = $this->object();
 5422:           $class = $object->contentClass();
 5423:           $this->ClassIdentifier = $class->attribute( 'identifier' );

There is no object for this result. But the object exists. The main problem is in method search of extension/ezfind/search/plugins/ezsolr/ezsolr.php.

$tmpNodeRowList = eZContentObjectTreeNode::fetch( $localNodeIDList, false, false );

The variable $tmpNodeRowList is sometimes an array of nodes (result of fetch are several nodes) and sometimes an array of attributes (result of fetch is one node).

for example an array of several nodes (print_r of $tmpNodeRowList):
[0] => array( "id" => 1, "contentclass_id" => 5, ...)
[1] => array( "id" => 2, "contentclass_id" => 5, ...)

an example of result of the fetch if there is an error
[id] => 1
[contentclass_id] => 5
...

If the result is one node the foreach loops about attributes and doesn't find the info for the object. Thatswhy the following code has no nodeList:

$nodeRowList[$nodeRow['node_id']] = $nodeRow;

An example of my output of $nodeRowList is:

Array
(
[4] => 47
[1] => 1
[2] => 2
[0] => 0
[F] => F1234
[7] => 7
[p] => products/...
[/] => /1/2/207/...
[a] => a:2:

[c] => class_product
[g] => ger-DE
)