Fix crash with budgets with no published phases

In this case, the duration of the budget cannot be determined, and the
application was crashing when trying to do so.

Now we're just returning `nil` as duration.

app/components/admin/budgets/duration_component.rb

@@ -10,7 +10,7 @@ class Admin::Budgets::DurationComponent < ApplicationComponent
   end
 
   def duration
-    distance_of_time_in_words(durable.starts_at, durable.ends_at)
+    distance_of_time_in_words(durable.starts_at, durable.ends_at) if durable.starts_at && durable.ends_at
   end
 
   private

app/models/budget.rb

@@ -72,11 +72,11 @@ class Budget < ApplicationRecord
   end
 
   def starts_at
-    phases.published.first.starts_at
+    phases.published.first&.starts_at
   end
 
   def ends_at
-    phases.published.last.ends_at
+    phases.published.last&.ends_at
   end
 
   def description

spec/components/admin/budgets/duration_component_spec.rb

@@ -43,6 +43,22 @@ describe Admin::Budgets::DurationComponent, type: :component do
 
       expect(page.text).to eq "about 1 year"
     end
+
+    it "is not defined when no end date is defined" do
+      durable = double(starts_at: Time.zone.local(2015, 8, 1, 12, 0, 0), ends_at: nil)
+
+      render Admin::Budgets::DurationComponent.new(durable).duration
+
+      expect(page.text).to be_empty
+    end
+
+    it "is not defined when no start date is defined" do
+      durable = double(starts_at: nil, ends_at: Time.zone.local(2016, 9, 30, 16, 30, 00))
+
+      render Admin::Budgets::DurationComponent.new(durable).duration
+
+      expect(page.text).to be_empty
+    end
   end
 
   attr_reader :content
@@ -52,6 +68,6 @@ describe Admin::Budgets::DurationComponent, type: :component do
   end
 
   def page
-    Capybara::Node::Simple.new(content)
+    Capybara::Node::Simple.new(content.to_s)
   end
 end

spec/components/admin/budgets/index_component_spec.rb

@@ -15,4 +15,13 @@ describe Admin::Budgets::IndexComponent, type: :component do
 
     expect(page.find("tr", text: "Not enabled phase")).to have_content "0/8"
   end
+
+  it "displays phase zero out of zero for budgets with no enabled phases" do
+    budget = create(:budget, name: "Without phases")
+    budget.phases.each { |phase| phase.update!(enabled: false) }
+
+    render_inline Admin::Budgets::IndexComponent.new(Budget.page(1))
+
+    expect(page.find("tr", text: "Without phases")).to have_content "0/0"
+  end
 end