System Information
Operating system: Windows-10-10.0.19042-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 496.49

Blender Version
Broken: version: 3.0.0 Release Candidate, branch: master, commit date: 2021-11-25 17:24, hash: rB2fb8c6805a98
Worked: version: 3.0.0 Beta, branch: master, commit date: 2021-11-07 23:44, hash: rB56ee96349dce (maybe also with a bit newer versions, that was the last one I was using before updating to the release candidate)

Short description of error
When creating custom python nodes that have only custom sockets, the node can't be dropped onto an existing link. This is not the case if the node has normal blender sockets, only with custom ones. It also doesn't happen if the node has blender and custom sockets as the blender sockets will be connected and the custom ones ignored.

Exact steps for others to reproduce the error

• Open the attached file and run the script in the text editor (this is the default custom node template with the blender internal sockets removed from the demo node)
• Drop the free floating node in the custom node editor onto the link between the other two nodes
• The node will not be linked up with the other nodes

If the same process is repeated in the version marked as working above the node is connected to the other two. If the same thing is done with the original default custom node template, the custom sockets will be ignored and the blender internal sockets will connect.