[BestPractice] Return an empty collection instead of null.

[github-actions]

Codacy ID: c88d177b01b83673a1ee79b5d7014d3f

File: TransactionProcessorACL/Factories/ModelFactory.cs
Line: 187
Rule: BestPractice (Warning)
Commit: 8772fcacea1f9b6d3db41ea2182a6f272a448a64

Message: Return an empty collection instead of null.

**Code Snippet:**
```csharp
                return null; 
```