Cleanup and fix tests.

app/Helpers/Collection/Account.php

@@ -16,11 +16,19 @@ class Account
     /** @var Collection */
     protected $accounts;
     /** @var string */
-    protected $difference;
+    protected $difference = '';
     /** @var string */
-    protected $end;
+    protected $end = '';
     /** @var string */
-    protected $start;
+    protected $start = '';
+
+    /**
+     * Account constructor.
+     */
+    public function __construct()
+    {
+        $this->accounts = new Collection;
+    }
 
     /**
      * @return Collection

app/Helpers/Collection/Balance.php

@@ -41,7 +41,7 @@ class Balance
      */
     public function getBalanceHeader(): BalanceHeader
     {
-        return $this->balanceHeader;
+        return $this->balanceHeader ?? new BalanceHeader;
     }
 
     /**