Update src/mcp/server/fastmcp/server.py

Co-authored-by: ihrpr <inna.hrpr@gmail.com>

Author: tim-watcha

src/mcp/server/fastmcp/server.py

@@ -597,7 +597,7 @@ def _normalize_path(self, mount_path: str, endpoint: str) -> str:
         # Combine paths
         return mount_path + endpoint
 
-    def sse_app(self, mount_path: str = "") -> Starlette:
+    def sse_app(self, mount_path: str | None = None) -> Starlette:
         """Return an instance of the SSE server app."""
         from starlette.middleware import Middleware
         from starlette.routing import Mount, Route