title: Angular2 Child Component with OPTIONAL Input
body: <h1>TLDR: Can an <code>@Input</code> be optional?</h1>
  
  <p>So i have this child component which is a modal for creating a Transaction (in bank terms), and i want to upgrade this modal to be create-or-update Transaction.</p>
  
  <p>Currently the modal is just a group of input fields and a submit button for creating.
  What i want to achieve is when this component gets a transaction as an input, it will be on 'edit-mode' and when it does not it will be on 'create-mode' (meaning the input field will be already filled with data in edit-mode and empty on create-mode)</p>
  
  <p>Can an <code>@Input transaction</code> somehow be optional?</p>