public Builder addOtherProperty(String key, String value) {
            Objects.requireNonNull(key, "Header property key must not be null");
            this.otherProperties.put(key, value);
            return this;
        }
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