Max number of headers is reached when invoking entities with variant encoding throwing an IllegalStateException

When invoking entities with a variant with an encoding, and an IllegalStateException is thrown after a while because request headers reaches to is maximum.

This is because setEntity on ClientInvocation adds the header to a map:
headers.header("Content-Encoding", v.getEncoding());

This should use a putSingle or a method headers.setEncoding should be created like setLanguage or setMediaType.