{{#each}} key

not-working.hbs

{{#each ratings key="rater" as |rating|}}
    <p>{{rating.rater}}</p>
    <p>{{rating.rating}}</p>
    <p>{{rating.confidence}}</p>
    <hr/>
    
{{else}}
    <p><em>No ratings for this employee</em></p>
{{/each}}

working.hbs

{{#each ratings key=rater as |rating|}}
    <p>{{rating.rater}}</p>
    <p>{{rating.rating}}</p>
    <p>{{rating.confidence}}</p>
    <hr/>
    
{{else}}
    <p><em>No ratings for this employee</em></p>
{{/each}}

I am running into an issue with with ember 1.13 and the key for an #each helper.

When using a quoted key I get the following error

Uncaught Error: You must provide a string key when callingyieldItem; you provided undefined

Why?