* depend on Logger to not contain mutable state.
     *
     * We could use Suppliers.memoizingSupplier here, but I micro-optimized to this implementation
     * to avoid the extra class for the lambda (and maybe more for memoizingSupplier itself) and the
     * indirection.
     *
     * One thing to *avoid* is a change to make each Logger user use memoizingSupplier directly:
     * That may introduce an extra class for each lambda (currently a dozen).