fix: added null check to prevent null reference exception when clicking properties

[marc-antoine-girard]

Description

Simply added a null check in RawReferenceDrawer.cs.

This fixes #21

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

[Thundernerd]

Would be great if you could update this branch with the latest changes. It's a bit hard to see what is affected at the moment

[Thundernerd]

Changed the title real quick to match conventional commits, that way it will be added in the changelog automatically.

Once again thanks for your work!