more verbose

src/main/java/com/elphel/imagej/ims/Imx5.java

@@ -192,6 +192,10 @@ public class Imx5 {
 			double[] quat,      // additional correction
 			double[] targ_quat, // quaternion to be corrected
 			boolean inverse) {
+		if ((quat==null) || (targ_quat == null)) {
+			System.out.println("applyQuaternionToQuaternion(): returning null");
+			return null;
+		}
 		Rotation ims_rot = new Rotation(quat[0],quat[1],quat[2],quat[3],true);
 		Rotation targ_rot = new Rotation(targ_quat[0],targ_quat[1],targ_quat[2],targ_quat[3],true);
 		Rotation rslt_rot;