public Builder addCustom(final Class... custom) {
            if (custom != null && custom.length > 0) {
                for (Class c : custom) {
                    addOrOverrideRegistration(c, id -> GryoTypeReg.of(c, id));
                }
            }
            return this;
        }
Register custom classes to serializes with gryo using default serialization. Note that calling this method
for a class that is already registered will override that registration.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/gryo/GryoMapper.java