Add link_url validation for cards when are header cards

Add link_url presence validation only when link_text is provided only for header cards.

In this case it makes sense to allow creating a "header card" without link_url, since
we can show the header without link text and without link url and it still does its
function.

app/models/widget/card.rb

@@ -9,7 +9,7 @@ class Widget::Card < ApplicationRecord
   include Globalizable
 
   validates_translation :title, presence: true
-  validates :link_url, presence: true, if: -> { !header? }
+  validates :link_url, presence: true, if: -> { !header? || link_text.present? }
 
   def self.header
     where(header: true)

spec/models/widget/card_spec.rb

@@ -25,6 +25,30 @@ describe Widget::Card do
         expect(card).not_to be_valid
       end
     end
+
+    context "header cards" do
+      it "is valid with no link_url and no link_text" do
+        header = build(:widget_card, :header, link_text: nil, link_url: nil)
+
+        expect(header).to be_valid
+      end
+
+      it "is not valid with link_text and no link_url" do
+        header = build(:widget_card, :header, link_text: "link text", link_url: nil)
+
+        expect(header).not_to be_valid
+        expect(header.errors.count).to be 1
+        expect(header.errors[:link_url].count).to be 1
+        expect(header.errors[:link_url].first).to eq "can't be blank"
+      end
+
+      it "is valid if link_text and link_url are both provided" do
+        header = build(:widget_card, :header, link_text: "Text link",
+                                              link_url: "https://consulproject.org")
+
+        expect(header).to be_valid
+      end
+    end
   end
 
   describe "#header" do