diff --git a/frappe/automation/doctype/assignment_rule/assignment_rule.py b/frappe/automation/doctype/assignment_rule/assignment_rule.py
index f6f789a65d..577d2cf4d8 100644
--- a/frappe/automation/doctype/assignment_rule/assignment_rule.py
+++ b/frappe/automation/doctype/assignment_rule/assignment_rule.py
@@ -109,12 +109,15 @@ class AssignmentRule(Document):
 
 	def safe_eval(self, fieldname, doc):
 		try:
-			return frappe.safe_eval(self.get(fieldname), None, doc)
+			if self.get(fieldname):
+				return frappe.safe_eval(self.get(fieldname), None, doc)
 		except Exception as e:
 			# when assignment fails, don't block the document as it may be
 			# a part of the email pulling
 			frappe.msgprint(frappe._('Auto assignment failed: {0}').format(str(e)), indicator = 'orange')
 
+		return False
+
 def get_assignments(doc):
 	return frappe.get_all('ToDo', fields = ['name', 'assignment_rule'], filters = dict(
 		reference_type = doc.get('doctype'),