fix: Membership - allow system users to create membership for existing Members

erpnext/non_profit/doctype/membership/membership.py

@@ -12,6 +12,7 @@ import erpnext
 
 class Membership(Document):
 	def validate(self):
+		if not self.member or not frappe.db.exists("Member", self.member):
 			member_name = frappe.get_value('Member', dict(email=frappe.session.user))
 
 			if not member_name: