diff --git a/server/src/api/controllers/Contacts/Contacts.ts b/server/src/api/controllers/Contacts/Contacts.ts
index 0ac82f44a..91a0c5f38 100644
--- a/server/src/api/controllers/Contacts/Contacts.ts
+++ b/server/src/api/controllers/Contacts/Contacts.ts
@@ -14,7 +14,7 @@ export default class ContactsController extends BaseController {
       check('company_name').optional().trim().escape(),
       check('display_name').exists().trim().escape(),
 
-      check('email').optional().isEmail().trim().escape(),
+      check('email').optional({ nullable: true }).normalizeEmail().isEmail(),
       check('website').optional().trim().escape(),
       check('work_phone').optional().trim().escape(),
       check('personal_phone').optional().trim().escape(),
diff --git a/server/src/api/controllers/Contacts/Customers.ts b/server/src/api/controllers/Contacts/Customers.ts
index e2acdd6f3..80481a57a 100644
--- a/server/src/api/controllers/Contacts/Customers.ts
+++ b/server/src/api/controllers/Contacts/Customers.ts
@@ -86,8 +86,8 @@ export default class CustomersController extends ContactsController {
    */
   get createCustomerDTOSchema() {
     return [
-      check('opening_balance').optional().isNumeric().toInt(),
-      check('opening_balance_at').optional().isISO8601(),
+      check('opening_balance').optional({ nullable: true }).isNumeric().toInt(),
+      check('opening_balance_at').optional({ nullable: true }).isISO8601(),
 
       check('currency_code').optional().trim().escape(),
     ];
diff --git a/server/src/api/middleware/ConvertEmptyStringsToNull.ts b/server/src/api/middleware/ConvertEmptyStringsToNull.ts
new file mode 100644
index 000000000..5099f28ef
--- /dev/null
+++ b/server/src/api/middleware/ConvertEmptyStringsToNull.ts
@@ -0,0 +1,8 @@
+import { Request, Response, NextFunction } from 'express';
+import { convertEmptyStringsToNull } from 'utils';
+
+export default (req: Request, res: Response, next: NextFunction) => {  
+  const transfomedBody = convertEmptyStringsToNull(req.body);
+  req.body = transfomedBody;
+  next();
+};
\ No newline at end of file
diff --git a/server/src/loaders/express.ts b/server/src/loaders/express.ts
index 435d6b0e6..242239de5 100644
--- a/server/src/loaders/express.ts
+++ b/server/src/loaders/express.ts
@@ -7,6 +7,7 @@ import i18n from 'i18n';
 import routes from 'api';
 import LoggerMiddleware from 'api/middleware/LoggerMiddleware';
 import AgendashController from 'api/controllers/Agendash';
+import ConvertEmptyStringsToNull from 'api/middleware/ConvertEmptyStringsToNull';
 import config from 'config';
 
 export default ({ app }) => {
@@ -36,6 +37,9 @@ export default ({ app }) => {
   // Logger middleware.
   app.use(LoggerMiddleware);
 
+  // Converts empty strings to null of request body.
+  app.use(ConvertEmptyStringsToNull);
+
   // Prefix all application routes.
   app.use(config.api.prefix, routes());
 
diff --git a/server/src/utils/index.js b/server/src/utils/index.js
index d2e08dfca..8c068a17a 100644
--- a/server/src/utils/index.js
+++ b/server/src/utils/index.js
@@ -195,6 +195,16 @@ const entriesAmountDiff = (newEntries, oldEntries, amountAttribute, idAttribute)
     .value();
 };
 
+const convertEmptyStringsToNull = (obj) => {
+  return _.mapValues(obj, (value, key) => {
+    return typeof value === 'string' ? 
+      value.trim() === '' ?
+      null :
+      value :
+      value;
+  });
+};
+
 export {
   hashPassword,
   origin,
@@ -214,4 +224,5 @@ export {
   getDefinedOptions,
 
   entriesAmountDiff,
+  convertEmptyStringsToNull,
 };