Fix warning when making document with clean (#467).
Fix warning when making document with clean (#467).

asakusafw/asakusafw,ashigeru/asakusafw,ashigeru/asakusafw,akirakw/asakusafw,akirakw/asakusafw,cocoatomo/asakusafw,asakusafw/asakusafw,cocoatomo/asakusafw