Symptoms

• The error was thrown on a WF while it makes a call to a Web Service method that connects to this Oracle DB
Extension Data: {"$type":"System.Runtime.Serialization.ExtensionDataObject, System.Runtime.Serialization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"}
ErrorMessage: Object reference not set to an instance of an object.
 

Diagnoses

It looks like the Service Instance was pointing to the wrong Environment
 

Resolution

Pointing Oracle Service instance to the correct environment resolved the issue.