@Deprecated
        public Builder allowOptionalNull(boolean allowOptionalNull) {
            if (allowOptionalNull) {
                return addFeature(Feature.ALLOW_OPTIONAL_NULLS);
            } else {
                features.remove(Feature.ALLOW_OPTIONAL_NULLS);
                return this;
            }
        }
Sets the strategy used to validate timestamps.

<p>By default, timestamps are validated using
{@link TimestampValidationStrategy#FORMAT}.

@param timestampValidationStrategy Timestamp validation strategy.
@return Returns the builder.
smithy-model/src/main/java/software/amazon/smithy/model/validation/NodeValidationVisitor.java