Create an Escalation Rule where the Assigned To Field Is Empty

Create an escalation rule.

1. Navigate to Setup > Support > Escalation Rules > New. 
2. In the Case Fields column, select Employee.
3. Enter a name for this rule.
4. Criteria is none of and highlight all the employee names in the Employee box.
5. Click Save.

Assign the escalation rule.

1. Navigate to Setup > Support > Manage Escalation Assignment > New.
2. Enter a Name. 
3. In the Configure Rule Definitions tab > Apply Rule field, select the rule created just created. 
4. In the Escalation Assignment tab, select the name of the support rep in the Escalatee field.
5. Click Add. 
6. Click Save.