Upgrade to OkHttp 3.8.

Quite disappointingly OkHttp 3.8's new requirement for a non-null message
ends up breaking Retrofit. Good excuse to get this release out at the
same time.

Explicitly handle wrapped, re-thrown exceptions from onComplete, onError.

Allowing skipping of params if the converters converted to a null

Add converters which facilitate the use of Optional.

Use custom exception type when triggering mock failure.

Since we omit the stack trace, this more clearly indicates the source being from Retrofit's mock behavior.

Both Java 8 and Guava are supported, just like in the adapters.

This is especially useful in the use of RxJava 2 as it does not allow null values in the stream. This means a return type declaration of Single<BodyType> might result in an NPE should a converter deserialize the response body into null. By adding one of these delegating converters before your normal converter, it allows you to use Single<Optional<BodyType>> to support this case.

Because Exceptions.throwIfFatal treats these as fatal, prior to this they would bubble up to the caller. This is either the thread uncaught exception handler which is fine, but in the case of async sources it would go to the library code invoking the async callback (like OkHttp's Call) which might swallow them.

Update to RxJava 1.3 and a stable Completable.

Add JSR 305 nullability annotations.

Upgrade to Checkstyle 7.7.

Allow Crawler to crawl urls that aren't present in the fetched urls set

Fix annotation docs to advertise string converters.

Make HttpException unchecked

Removal of Unnecessary Creation of String Builder

Fix typo in CHANGELOG

if typeArguments has length 0 there is no point to create stringBuilder for that. that condition check needs to happen before stringBuilder creation.

Add error-prone compiler.

Use array instead of varargs in override signature.

Unify HttpException into a single shared type.