DependencyWalker.DiscoverDependencies fails with System.ArgumentException: Item has already been added.

We hit this when we had a few old stored procedures referring to the same dropped table with different casing for database name. I see commented out code at https://github.com/microsoft/sqlmanagementobjects/blob/main/src/Microsoft/SqlServer/Management/Smo/DependencyTree.cs#L198 that might have fixed this issue, not sure why it's been commented out though.

Microsoft.SqlServer.Management.Smo.FailedOperationException: Discover dependencies failed. 
 ---> System.ArgumentException: Item has already been added. Key in dictionary: 'Server[@Name='SERVER']/Database[@Name='database']/UnresolvedEntity[@Name='nonexisting_table' and @Schema='dbo']'  Key being added: 'Server[@Name='SERVER']/Database[@Name='DATABASE']/UnresolvedEntity[@Name='nonexisting_table' and @Schema='dbo']'
   at Microsoft.SqlServer.Management.Smo.DependencyTree..ctor(Urn[] urns, DependencyChainCollection dependencies, Boolean fParents, Server server)
   at Microsoft.SqlServer.Management.Smo.DependencyWalker.DiscoverDependencies(Urn[] urns, Boolean parents)

从 src/Microsoft/SqlServer/Management/Smo/DependencyTree.cs 第 198 行附近开始，跟踪 DependencyWalker.DiscoverDependencies，了解未解析实体是如何作为键的。使用仅数据库名称大小写不同的引用重现该故障，然后评估已注释掉的逻辑。当等效的未解析引用使用不同的大小写时，依赖项发现不再抛出异常，即表示完成。