SRFI 16 and R6RS both allow case-lambda with no cases in the syntax; the current R7RS-small draft does not. Technically this should be editorial, but I thought we should have a chance to vote on whether or not to allow it. The R6RS-editors list allowed it for the sake of mechanically generated code, but actually invoking such a case-lambda inevitably provokes an error, whether syntax or "no case matches", so it seems useless to me.
Treating as editorial.