Question:

If a Picklist type field is set as required, Salesforce does not display the --None-- value in its drop-down list.

Even though the Picklist type field on the Call Discussion object is set as required, the --None-- value displays in its drop-down list on the Call Discussion section of Call page.

Answer:

This is currently working as designed.

Although Salesforce does not display --None-- when a Picklist type field is set as required, Veeva makes it explicit that a user needs to enter a value for a required field. 

Related Documentation:

N/A

Thank you