diff --git a/gns3server/compute/qemu/__init__.py b/gns3server/compute/qemu/__init__.py
index 562f684b..d377fd6e 100644
--- a/gns3server/compute/qemu/__init__.py
+++ b/gns3server/compute/qemu/__init__.py
@@ -214,7 +214,7 @@ class Qemu(BaseManager):
                             return version
                 except (UnicodeDecodeError, OSError) as e:
                     log.warning("could not read {}: {}".format(version_file, e))
-            return None
+            return ""
         else:
             try:
                 output = await subprocess_check_output(qemu_path, "-version", "-nographic")