What occurs if there is no sys_popup view defined for the [sys_user] table and an agent hovers over the reference icon next to the caller field?

When no sys_popup view is defined for the [sys_user] table, hovering over the reference icon next to the caller field will result in the default view of the User form being displayed. This is because the system seeks a way to display relevant user data when the predefined popup option is not available.

In the case of the absence of a sys_popup, the ServiceNow platform resorts to its basic display settings, which leads it to present a standard form for the user. This form is designed to show comprehensive information about the user, making it accessible and informative for agents interacting with it.

Moreover, the other options do not accurately represent how the system behaves in this scenario. There is no occurrence of an error message popping up, nor is there a restriction to dot-walked fields. Additionally, even without a specifically defined sys_popup, the reference icon will still be present as it serves as a navigational tool for accessing user details, ensuring a consistent user interface.