Only apply custom umask if NB_UMASK is set

base-notebook/Dockerfile

@@ -35,7 +35,6 @@ ENV CONDA_DIR=/opt/conda \
     NB_USER=$NB_USER \
     NB_UID=$NB_UID \
     NB_GID=$NB_GID \
-    NB_UMASK=0022 \
     LC_ALL=en_US.UTF-8 \
     LANG=en_US.UTF-8 \
     LANGUAGE=en_US.UTF-8

base-notebook/jupyter_notebook_config.py

@@ -38,5 +38,7 @@ if 'GEN_CERT' in os.environ:
     os.chmod(pem_file, stat.S_IRUSR | stat.S_IWUSR)
     c.NotebookApp.certfile = pem_file
 
-# Change default umask if set using flag
-os.umask(int(os.environ['NB_UMASK'], 8))
+# Change default umask for all subprocesses of the notebook server if set in
+# the environment
+if 'NB_UMASK' in os.environ:
+    os.umask(int(os.environ['NB_UMASK'], 8))