allow empty strings

packages/app/src/server/models/revision.js

@@ -16,7 +16,6 @@ module.exports = function(crowi) {
     pageId: { type: ObjectId, required: true, index: true },
     body: {
       type: String,
-      required: true,
       get: (data) => {
       // replace CR/CRLF to LF above v3.1.5
       // see https://github.com/weseek/growi/issues/463