How can Sentinel-1 images be un-flipped?

TOPSAR_Slices_Coreg_coherence.xml (7.0 KB)

The attachement showes the graph builder to first assemble two masters and two slaves and then generate coherence. But the problem is that I get the error when I open the image in SNAP as bellow:
java.Lang.NullPointerException.
I I am using a machine with 64GB RAM.

Cheers,
Vahid.