Issue #140: check for an empty scheme file.

map_machine/mapper.py

@@ -267,7 +267,9 @@ def render_map(arguments: argparse.Namespace) -> None:
     if scheme_path is None:
         fatal(f"Scheme `{arguments.scheme}` not found.")
 
-    scheme: Scheme = Scheme.from_file(scheme_path)
+    scheme: Optional[Scheme] = Scheme.from_file(scheme_path)
+    if scheme is None:
+        fatal(f"Failed to load scheme from `{arguments.scheme}`.")
 
     configuration: MapConfiguration = MapConfiguration.from_options(
         scheme, arguments, float(arguments.zoom)

map_machine/scheme.py

@@ -363,15 +363,20 @@ class Scheme:
         self.cache: dict[str, tuple[IconSet, int]] = {}
 
     @classmethod
-    def from_file(cls, file_name: Path) -> "Scheme":
+    def from_file(cls, file_name: Path) -> Optional["Scheme"]:
         """
         :param file_name: name of the scheme file with tags, colors, and tag key
             specification
         """
         with file_name.open(encoding="utf-8") as input_file:
+            try:
                 content: dict[str, Any] = yaml.load(
                     input_file.read(), Loader=yaml.FullLoader
                 )
+            except yaml.YAMLError:
+                return None
+            if not content:
+                return cls({})
             return cls(content)
 
     def get_color(self, color: str) -> Color: