How to reproduce:
1. Create a new Unity project and install the Unity Cloud Collaboration package
2. Import the "Creating and reading basic annotations" sample
3. Go to Collaboration Samples -> Create and Read Annotations
4. Enter a "Space"/"Enter" and submit a new annotation
5. Observe the annotations list
Expected results: The message field's submit action is blocked or ignored when the text is a new line or whitespace-only
Actual results: An annotation with an empty message is created and appears in the list
Reproducible with: 1.0.1 (6000.7.0a5)
Reproducible on: macOS Tahoe 26 (M1)
Not reproducible on: No other environment tested