Reject blank & null vallues when generating PDF styles

[Lubosky]

📝 A short description of the changes

Reject blank & nil values from being picked by PDF generator.

🔗 Link to the relevant story (or stories)

Asana card here: https://app.asana.com/0/1200504523179343/1207645684540462/f
AppSignal error here: https://appsignal.com/bit-zesty/sites/601bfb8714ad665fb298effe/exceptions/incidents/3606/samples/601bfb8714ad665fb298effe-664236946902935182917192454001

Deployment implications

Done

✅ Checklist

• Features that cannot go live are behind a feature flag/env var or specify deploy date and open PR as draft
• I have checked that commit messages make sense and explain the reasoning for each change
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have squashed any unnecessary or part-finished commits

🖼️ Screenshots (if appropriate - no PII/Prod data):