"Send as" popup isn't readable

Summary

The "Send as" popup is difficult to read, especially because of the background + in some cases (the identity has no name set?) it's written null before the email address.

Description

What is the current behavior?

The "Send as" popup has white and grey background

What is the improved behavior?

Improve UI and if an element is set as null in database, display nothing instead of null.

What does it bring?

Better readibility

Examples

Validation

Checklist

• License
• Translations
• Documentation
• Test plan

Completed mockup design

Link to Figma project (done) - https://www.figma.com/file/IYFNR6xuNZXd1hqGl6itT6/02-Mail-app-%F0%9F%94%A8?node-id=919%3A2994

/cc @fahim44 @rana.narin @aude.m