add server to monorepo.

packages/server/src/api/middleware/ConvertEmptyStringsToNull.ts

@@ -0,0 +1,13 @@
+import { Request, Response, NextFunction } from 'express';
+import deepMap from 'deep-map';
+import { convertEmptyStringToNull } from 'utils';
+
+function convertEmptyStringsToNull(data) {
+  return deepMap(data, (value) => convertEmptyStringToNull(value));
+}
+
+export default (req: Request, res: Response, next: NextFunction) => {  
+  const transfomedBody = convertEmptyStringsToNull(req.body);
+  req.body = transfomedBody;
+  next();
+};