validate content-type set as constant/required while @body or @bodyRoot value is optional?

if the spec contains the following for an operation:

```
model Bar {
baz: string;
}

op foo(
@doc("Type of content")
@header("content-type")
contentType: "application/json; odata=minimalmetadata";

@doc("The body.")
@body
body?: Bar;
): void;
```

Do we allow content-type to be required if the body is not or should we validate this?