diff --git a/requirements-dev.txt b/requirements-dev.txt
index 2d28c2da90..db69f9e959 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -11,7 +11,7 @@ astroid>=2.15,<3
 sphinx-autodoc-typehints>=1.24.0,<2
 sphinxcontrib-autoprogram==0.1.8
 cwltest>=2.2.20211116163652
-mypy==1.5.1
+mypy==1.6.1
 types-requests
 types-setuptools
 types-boto
diff --git a/src/toil/server/cli/wes_cwl_runner.py b/src/toil/server/cli/wes_cwl_runner.py
index 7387f2e23d..67c2e0103f 100644
--- a/src/toil/server/cli/wes_cwl_runner.py
+++ b/src/toil/server/cli/wes_cwl_runner.py
@@ -396,7 +396,7 @@ def submit_run(client: WESClientWithWorkflowEngineParameters,
         input_file,
         attachments=attachments,
         workflow_engine_parameters=engine_options)
-    return run_result.get("run_id", None)
+    return str(run_result["run_id"])
 
 
 def poll_run(client: WESClientWithWorkflowEngineParameters, run_id: str) -> bool: