Index: Classes/Property/Mapper.php
===================================================================
--- Classes/Property/Mapper.php	(Revision 2529)
+++ Classes/Property/Mapper.php	(Arbeitskopie)
@@ -260,7 +260,7 @@
 				}
 			}
 		} else {
-			if (is_numeric($propertyValue)) {
+			if (is_numeric($propertyValue) && $propertyValue !== 0) {
 				$propertyValue = $this->findObjectByUid($targetType, $propertyValue);
 				if ($propertyValue === FALSE) {
 					$this->mappingResults->addError(new Tx_Extbase_Error_Error('Querying the repository for the specified object with UUID ' . $propertyValue . ' was not successful.' , 1249379517), $propertyName);
@@ -288,6 +288,8 @@
 						$propertyValue = NULL;
 					}
 				}
+			} elseif (is_string($propertyValue) && t3lib_div::inList('0','','NULL', $propertyValue)) {
+				$propertyValue = NULL;
 			} else {
 				throw new InvalidArgumentException('transformToObject() accepts only numeric values and arrays.', 1251814355);
 			}