app/models/member.rb

@@ -1,5 +1,5 @@
 class Member < ApplicationRecord
-  has_many :incomes
+  has_many :incomes, dependent: :destroy
 
   def income
     incomes.sum(&:amount)
@@ -15,6 +15,8 @@ class Member < ApplicationRecord
 
   def burden_percent
     ((Income.total - others_included_income) / Income.total).round(2)
+  rescue
+    0
   end
 
   def burden_amount(total_amount: Expense.monthly_total)