public ApimanEventHeaders build() {
            Validate.notBlank(id, "ID field must be set and not blank");
            Objects.requireNonNull(source, "Source must be set");
            //Objects.requireNonNull(type, "Type must be set");
            //Objects.requireNonNull(subject, "Subject must be set");
            Objects.requireNonNull(time, "Time must be set");
            // Preconditions.checkArgument(eventVersion > 0, "Version must be > 0");

            return new ApimanEventHeaders(
                 id,
                 source,
                 type,
                 subject,
                 time,
                 eventVersion,
                 otherProperties
            );
        }
Version of the event these headers are associated with. If you do not set this then the
class' <tt>@EventVersion</tt> annotation will be used.
manager/api/beans/src/main/java/io/apiman/manager/api/beans/events/ApimanEventHeaders.java