Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You used path match with a pattern that has no parameters, and the engine pointed out that the call has nothing to say. Here is how path match works. You give it a pattern and a path. If they match completely, it answers with a map of the bound parameters. A parameter is a segment written with a colon and a name, like colon id. The match then tells you what that segment turned out to be. But if your pattern has no colon segments, there is nothing to bind. And an empty map is not allowed to exist in rush, so there is no sensible answer to give. The engine refuses and shows your pattern. The fix depends on what you really wanted. If you only need to know whether two paths are the same, just compare the texts with the double equals. That answers true or false, plainly. If you wanted to pull out a piece, like a user id, then add a colon segment to the pattern, and path match will hand it back to you.
Text from the Rush engine's error catalogue.