fix: add None guards for pyright reportOptionalMemberAccess

Author: g97iulio1609

tests/client/test_auth.py

@@ -2289,13 +2289,15 @@ def test_merge_disjoint_scopes(self):
         from mcp.client.auth.utils import merge_scopes
 
         result = merge_scopes("init", "mcp:tools:read")
+        assert result is not None
         scopes = set(result.split())
         assert scopes == {"init", "mcp:tools:read"}
 
     def test_merge_overlapping_scopes_deduplicates(self):
         from mcp.client.auth.utils import merge_scopes
 
         result = merge_scopes("init mcp:tools:read", "mcp:tools:read mcp:tools:write")
+        assert result is not None
         scopes = set(result.split())
         assert scopes == {"init", "mcp:tools:read", "mcp:tools:write"}