fix: fail to load budget page due to nan in category % calculation

app/models/category.rb

@@ -32,7 +32,10 @@ def in_spending?(month_date)
   end
 
   def spent_percentage_in_month(month_date)
-    (spent_amount_cents_in_month(month_date).to_f / assigned_amount_in(month_date).cents.to_f) * 100.0
+    assigned_amount_in_month_cents = assigned_amount_in(month_date).cents.to_f
+    return assigned_amount_in_month_cents if assigned_amount_in_month_cents.zero?
+
+    (spent_amount_cents_in_month(month_date).to_f / assigned_amount_in_month_cents ) * 100.0
   end
 
 

test/models/category_test.rb

@@ -123,6 +123,17 @@ class CategoryTest < ActiveSupport::TestCase
     assert_equal(@category.spent_percentage_in_month(beginning_of_month), (20000.to_f / 30000.to_f) * 100)
   end
 
+  test "spent_percentage returns 0 when the assigned amount is 0" do
+    movement_date = Time.now.utc
+    beginning_of_month = movement_date.beginning_of_month
+
+    movement_1 = Movement.create!(payer: "payer_1", amount_cents: -10000, account: @account, category: @category, created_at: movement_date)
+    movement_2 = Movement.create!(payer: "payer_2", amount_cents: -10000, account: @account, category: @category, created_at: movement_date)
+    MonthlyAssignment.create!(category: @category, start_date: beginning_of_month, end_date: beginning_of_month.next_month, amount: Money.new(0, "EUR")) 
+
+    assert_equal(@category.spent_percentage_in_month(beginning_of_month), 0.0)
+  end
+
   test "in_spending? returns true when spent_percentage is GREATER than 0%" do
     movement_date = Time.now.utc
     beginning_of_month = movement_date.beginning_of_month