Merge pull request #1242 from camlloyd/empty_zip_fix

fix: avoid saving empty .zip archive

Author: carsen-stringer

cellpose/io.py

@@ -723,6 +723,10 @@ def save_rois(masks, file_name, multiprocessing=None, prefix='', pad=False):
     Returns:
         None
     """
+    if masks.max() == 0:
+        io_logger.warning("no masks found, will not save ImageJ ROIs to .zip archive")
+        return
+
     outlines = utils.outlines_list(masks, multiprocessing=multiprocessing)
 
     n_digits = int(np.floor(np.log10(masks.max()))+1) if pad else 0