Sending PUT request to the host's API that updates multiple NICs and removes the primary one causes internal server error. Note that it happens only when the request updates more than one interface.
Example json to reproduce the error:

{"host" => {
    "interfaces_attributes" => [
        [0] {
                 "id" => 26,
            "primary" => false
        },
        [1] {
                 "id" => 55,
            "primary" => false
        }
    ]
}}

This is probably very rare case and our CLI prevents from it but we should respond with 402 an error message rather than 500 and a backtrace.