`stellar tx sign` shouldn't require an RPC URL

[drebelsky]

What version are you using?

$ stellar --version
stellar 25.2.0
stellar-xdr 25.0.0 (dc9f40fcb83c3054341f70b65a2222073369b37b)
xdr curr (0a621ec7811db000a60efae5b35f78dee3aa2533)

What did you do?

$ echo $TX                                                                                          
AAAAAgAAAAAnEWb4nxMsQhdnS16MqBxwItF3X/JNRkfxu8eyEQyfegAAAGQAAAAAAAAAAQAAAAAAAAAAAAAAAQAAAAAAAAABAAAAABk++lrW4HlZwaWwYdYvJPCil1ibyI/VTH6W
Kda2sOC+AAAAAAAAAAAAAABkAAAAAAAAAAA=
$ SK=SBKGK43UIFRWG33VNZ2C2MJOFYXC4LROFYXC4LROFYXC4LROFYXC4MRC 
$ echo $TX | stellar tx sign --network-passphrase "specified manually" --sign-with-key $SK
❌ error: network passphrase is used but rpc-url is missing, use `--rpc-url` or `STELLAR_RPC_URL`
$ echo $TX | stellar tx sign --network-passphrase "specified manually" --sign-with-key $SK --rpc-url ""
ℹ️  Signing transaction: 623210609fa16271fdb8adf873d5fe1f0199605efd7a481652277bc6e75b7b75
AAAAAgAAAAAnEWb4nxMsQhdnS16MqBxwItF3X/JNRkfxu8eyEQyfegAAAGQAAAAAAAAAAQAAAAAAAAAAAAAAAQAAAAAAAAABAAAAABk++lrW4HlZwaWwYdYvJPCil1ibyI/VTH6W
Kda2sOC+AAAAAAAAAAAAAABkAAAAAAAAAAERDJ96AAAAQBsSroaclA2LM5C6BsFKIg4KN+ERZdTcKdeN2CvouSfY6Q8QPFpVA3OIwrzpSf2czVlRKyy0H4Z/OKVXHGaKwws=

What did you expect to see?/What did you see instead?

I would've expected the first stellar tx sign command to work without needing to specify an RPC URL because as the second one indicates, RPC doesn't seem to be necessary for transaction signing.