code: public void copyVendorExtensions(Schema source, Schema target) {
          if (source.getExtensions() != null) {
              Map<String, Object> vendorExtensions = source.getExtensions();
              for (String extName : vendorExtensions.keySet()) {
                  ((SchemaImpl) target).addExtension_compat(extName, vendorExtensions.get(extName));
              }
          }
      }
docs: Copy vendor extensions from Property to another Property
  
  @param source source property
  @param target target property