Suppress noisy empty debug messages

src/ocrmypdf/exec/ghostscript.py

@@ -166,7 +166,7 @@ def rasterize_pdf(
         p = run(args_gs, stdout=PIPE, stderr=STDOUT, universal_newlines=True)
         if _gs_error_reported(p.stdout):
             log.error(p.stdout)
-        else:
+        elif p.stdout:
             log.debug(p.stdout)
 
         if p.returncode != 0:

src/ocrmypdf/optimize.py

@@ -276,7 +276,8 @@ def _produce_jbig2_images(jbig2_groups, root, log, options):
         ) as pbar:
             for future in concurrent.futures.as_completed(futures):
                 proc = future.result()
-                log.debug(proc.stderr.decode())
+                if proc.stderr:
+                    log.debug(proc.stderr.decode())
                 pbar.update()