fix mypy errors

src/dvc_render/markdown.py

@@ -1,5 +1,5 @@
 from pathlib import Path
-from typing import TYPE_CHECKING, List, Optional, Union
+from typing import TYPE_CHECKING, List, Optional
 
 from .exceptions import MissingPlaceholderError
 
@@ -48,7 +48,7 @@ def render_markdown(
     renderers: List["Renderer"],
     output_file: Optional["StrPath"] = None,
     template_path: Optional["StrPath"] = None,
-) -> Union["StrPath", "str"]:
+) -> "StrPath":
     "User renderers to fill an Markdown template and write to path."
     output_path = None
     if output_file:
@@ -65,7 +65,7 @@ def render_markdown(
     for renderer in renderers:
         document.with_element(renderer.generate_markdown(report_path=output_path))
 
-    if output_file:
+    if output_file and output_path:
         output_path.write_text(document.embed(), encoding="utf8")
 
         return output_file

src/dvc_render/vega.py

@@ -104,12 +104,13 @@ def generate_markdown(self, report_path=None) -> str:
 
         data = list_dict_to_dict_list(self.datapoints)
         if data:
-            output_file = io.BytesIO()
             if report_path:
                 report_folder = Path(report_path).parent
                 output_file = report_folder / self.name
                 output_file = output_file.with_suffix(".png")
                 output_file.parent.mkdir(exist_ok=True, parents=True)
+            else:
+                output_file = io.BytesIO()  # type: ignore
 
             x = self.properties.get("x")
             y = self.properties.get("y")
@@ -127,7 +128,9 @@ def generate_markdown(self, report_path=None) -> str:
             if report_path:
                 return f"\n![{self.name}]({output_file.relative_to(report_folder)})"
 
-            base64_str = base64.b64encode(output_file.getvalue()).decode()
+            base64_str = base64.b64encode(
+                output_file.getvalue()
+            ).decode()  # type: ignore
             src = f"data:image/png;base64,{base64_str}"
 
             return f"\n![{self.name}]({src})"