SARSim Terrain Correction will not operate after parameter selections

After selection of an external DEM in SARSim Terrain Correction a missing required field is noted:
“4-SARSim Terrain-Correciton: [name] is an empty string”.

After selection of “Apply radiometric normalization”:
The first error after selection of a different tab is:
"4-SARSim Terrain-Correciton: org.esa.snap.framework.gpf.OperatorException due to java.lang.NullPointerException
After selection of a second tab:
“4-SARSim Terrain-Correciton: Please select output band for terrain correct image”