private Lookup legacyReadLookup() throws NoSuchFieldException, IllegalAccessException {
    Field field = Lookup.class.getDeclaredField("IMPL_LOOKUP");
    field.setAccessible(true);
    Lookup lookup = (Lookup) field.get(null);
    return lookup;
  }
equivalent to:

<pre>
return MethodHandles.privateLookupIn(declaringClass, MethodHandles.lookup());
</pre>

@param declaringClass
@return
@throws IllegalAccessException
@throws InvocationTargetException
@throws NoSuchMethodException
core/src/main/java/feign/DefaultMethodHandler.java