http: improve error message with null header

Which @angular/* package(s) are relevant/related to the feature request?

No response

Description

When a header value of an HTTP call is null we throw a TypeError: Cannot read properties of null (reading 'length').

That's accurate and could be more useful if we also specify the header with null value.

You can find a reproduction on StackBlitz.

Based on a discussion on Twitter here.

Proposed solution

Throw an error Cannot read the "length" property of the header "bar" because it has value null

Alternatives considered

Stricter typings of the headers so that we can show a type error.