diff --git a/src/python/jw/pkg/lib/ExecContext.py b/src/python/jw/pkg/lib/ExecContext.py
index af3035cc..0fab4a89 100644
--- a/src/python/jw/pkg/lib/ExecContext.py
+++ b/src/python/jw/pkg/lib/ExecContext.py
@@ -202,6 +202,8 @@ class ExecContext(abc.ABC):
         ret = Result(None, None, 1)
         if opts is None:
             opts = {}
+        if mod_env is None:
+            mod_env = {}
         with self.CallContext(self, title=title, cmd=cmd, cmd_input=cmd_input, wd=wd,
                               log_prefix='|', interactive=None, throw=throw, verbose=verbose) as cc:
             try: