chore: update mypy to 1.9.0 and resolve one issue

mypy 1.9.0 flagged one issue in the code. Resolve the issue. Current
unit tests already check that a `None` value returns `text/plain`. So
function is still working as expected.

.pre-commit-config.yaml

@@ -30,7 +30,7 @@ repos:
           - requests-toolbelt==1.0.0
         files: 'gitlab/'
   - repo: https://github.com/pre-commit/mirrors-mypy
-    rev: v1.8.0
+    rev: v1.9.0
     hooks:
       - id: mypy
         args: []

gitlab/utils.py

@@ -18,7 +18,8 @@ def __call__(self, chunk: Any) -> None:
 
 def get_content_type(content_type: Optional[str]) -> str:
     message = email.message.Message()
-    message["content-type"] = content_type
+    if content_type is not None:
+        message["content-type"] = content_type
 
     return message.get_content_type()
 

requirements-lint.txt

@@ -4,7 +4,7 @@ black==24.3.0
 commitizen==3.16.0
 flake8==7.0.0
 isort==5.13.2
-mypy==1.8.0
+mypy==1.9.0
 pylint==3.1.0
 pytest==8.0.2
 responses==0.25.0