public HopSpec setRecipient(int i, String recipient) {
        recipients.set(i, recipient);
        return this;
    }
Sets the recipient at the given index.

@param i         The index at which to set the recipient.
@param recipient The recipient to set.
@return This, to allow chaining.
messagebus/src/main/java/com/yahoo/messagebus/routing/HopSpec.java