refactor: use list[str] | None for dependencies parameter

Matches the convention used by other sequence parameters in the same
constructor (icons, tools) and avoids the Collection[str] footgun where
a bare string like dependencies="pandas" would be iterated as chars.

Author: maxisbey

src/mcp/server/mcpserver/server.py

@@ -6,7 +6,7 @@
 import inspect
 import json
 import re
-from collections.abc import AsyncIterator, Awaitable, Callable, Collection, Iterable, Sequence
+from collections.abc import AsyncIterator, Awaitable, Callable, Iterable, Sequence
 from contextlib import AbstractAsyncContextManager, asynccontextmanager
 from typing import Any, Generic, Literal, TypeVar, overload
 
@@ -145,7 +145,7 @@ def __init__(
         warn_on_duplicate_resources: bool = True,
         warn_on_duplicate_tools: bool = True,
         warn_on_duplicate_prompts: bool = True,
-        dependencies: Collection[str] = (),
+        dependencies: list[str] | None = None,
         lifespan: Callable[[MCPServer[LifespanResultT]], AbstractAsyncContextManager[LifespanResultT]] | None = None,
         auth: AuthSettings | None = None,
     ):
@@ -155,7 +155,7 @@ def __init__(
             warn_on_duplicate_resources=warn_on_duplicate_resources,
             warn_on_duplicate_tools=warn_on_duplicate_tools,
             warn_on_duplicate_prompts=warn_on_duplicate_prompts,
-            dependencies=list(dependencies),
+            dependencies=dependencies or [],
             lifespan=lifespan,
             auth=auth,
         )