@Override
    public Void visitArray(ArrayType t, TypeMirrorSet visiting) {
      return t.getComponentType().accept(this, visiting);
    }
Check that the return type and parameter types of the given method are all defined, and arrange
to defer processing until the next round if not.

@throws MissingTypeException if the return type or a parameter type of the given method is
    undefined
value/src/main/java/com/google/auto/value/processor/MissingTypes.java