Nashorn can't complete test suite

[lance]

Nashorn considers JavaThing#op(String arg) and JavaThing#op(CharSequence arg) to be ambiguous. I think this is probably a bug in nashorn, since it should at least not fail. However tests begin failing with error messages like:

SEVERE: Exception in Nashorn JavaScript verticle
java.lang.RuntimeException: java.lang.NoSuchMethodException: Can't unambiguously select between fixed arity signatures [(java.lang.String, java.lang.String), (java.lang.CharSequence, java.lang.CharSequence)] of the method org.vertx.java.core.http.impl.HttpHeadersAdapter.set for argument types [java.lang.String, jdk.nashorn.internal.runtime.ConsString]
at org.vertx.java.core.Handler$$NashornJavaAdapter.handle(Unknown Source)
at org.vertx.java.core.http.impl.DefaultHttpServer$4$1.run(DefaultHttpServer.java:250)