Ensure null values are not passed to trim() (#2889)

Author: mattdavenport

app/code/core/Mage/Eav/Model/Entity/Attribute/Abstract.php

@@ -627,7 +627,7 @@ public function getBackendTable()
             if ($this->isStatic()) {
                 $this->_dataTable = $this->getEntityType()->getValueTablePrefix();
             } else {
-                $backendTable = trim($this->_getData('backend_table'));
+                $backendTable = trim((string)$this->_getData('backend_table'));
                 if (empty($backendTable)) {
                     $entityTable  = [$this->getEntity()->getEntityTablePrefix(), $this->getBackendType()];
                     $backendTable = $this->getResource()->getTable($entityTable);