Expressions in parameters are destroyed by url-encoding during url creation in AbstractEndpointBuilder (using little non-sensical example to make reproduction setup easier).
will be translated by AbstractEndpointBuilder#computeUri (which uses URISupport#createQueryString) to
This will, of course, throw exception on endpoint creation.
For some reason, thrown exception is url-decoded, so parameter names will look OK, even when they are broken (this makes the error more difficult to spot)
Enclosing expressions in RAW(..), fixes the issue, it is however quite suboptimal.
Following workaround will work: