t5091.scala:8: error: recursive value xxx needs type
    val param = bar(xxx)
                    ^
t5091.scala:7: warning: type-checking the invocation of method foo checks if the named argument expression 'param = ...' is a valid assignment
in the current scope. The resulting type inference error (see above) can be fixed by providing an explicit type in the local definition for param.
    val xxx = foo(param = null)
                        ^
one warning found
one error found