According to the SRFI-16 specification, a case-lambda form includes zero
or more <clause>s:

    (CASE-LAMBDA <clause> ...)

However, the reference implementation defines case-lambda to accept only
one or more clauses.

I am not sure what should be done about this bug, however the R6RS
standard libraries document includes a correct implementation.

http://www.r6rs.org/final/html/r6rs-lib/r6rs-lib-Z-H-6.html#node_idx_262

David