Setting Domain_Search_Object_Category to empty string

Description:

I am using open LDAP with rocket.chat. Therefore I need to set the Domain Search Object Category to "". It's not possible to configure this setting via environment variables, because Nodejs doesn't set environment variables which are equal to the empty string in the process.env object.

Server Setup Information:

• Version of Rocket.Chat Server: 0.57.2
• Operating System: Ubuntu 16.04
• Deployment Method(snap/docker/tar/etc): docker
• Number of Running Instances: 1
• DB Replicaset Oplog:
• Node Version: v4.2.6

Steps to Reproduce:

1. Start with an empty MongoDB Intance
2. Set the OVERWRITE_SETTING_LDAP_Domain_Search_Object_Category="" env variable before starting the app.
3. Start the App
4. Check the value of Domain Search Object Category in the LDAP settings.

Expected behavior:

The Domain Search Object Category property should be set to an empty value.

Actual behavior:

The Domain Search Object Category is set to the default value.

The code relevant for loading the environment variables can be found here.

I've tested the Nodejs environment variable loading and it seems, that an env variable set to the empty string will not be loaded into the process.env object.