MT#57752 Removing SecretKey for mail2fax doesn't work

Change-Id: I48d0a0cff435a3f36d49aded8401ebdf461f05c8
(cherry picked from commit 8d73ce0997)

src/components/pages/FaxSettings/CscMailToFaxSettings.vue

@@ -301,6 +301,9 @@ export default {
         },
         async setChangedData (field, value, beforeUpdateUI = () => {}) {
             try {
+                if (field === 'secret_key') {
+                    value = value === '' ? null : value
+                }
                 await this.mailToFaxSettingsUpdateAction({ field, value })
                 beforeUpdateUI()
                 this.updateDataFromStore()