Reproduce:
Call tasks center module, click on the gray icon
"open in new window" (right top corner)

Error:
UnexpectedValueException thrown in file
\typo3\mod.php in line 55.

Change-Id: Ic94913f2bee2019c9be1954fc9ff78f90b8c5f84
Fixes: #40154
Related: #40095
Releases: 6.0
Reviewed-on: http://review.typo3.org/14063
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn