[Bug] LinkTo do not generates href when @model is defined as undefined

### 🐞 Describe the Bug
When using LinkTo in a component and we want `@model` to be optional, the href is not being generated if no model is provided.

### 🔬 Minimal Reproduction
https://gist.github.com/rogeraraujo90/bc68849c7bf81bba7e0127706c690111

### 😕 Actual Behavior
The href is generated as `#`

### 🤔 Expected Behavior
The href should be generated correctly to the provided route.

PS: If I remove the `@model` from the LinkTo component the href is generated correctly in my Ember version. Is not working well on Twiddle.

### 🌍 Environment

- Ember: 3.28.8
- Node.js/npm: 14.16.1
- OS: Windows
- Browser: Brave (chromium based)

### ➕ Additional Context
Even though I couldn't fix the problem in the twiddle, in my project I could by removing the `@model` param in my component. But this is not ideal because since this is a component, I would like to have the possibility to pass a model or not.

Discord discussion: https://discord.com/channels/480462759797063690/483601670685720591/943929878108069978