public DocPath append(final DocPath otherPath) {
        if (otherPath == null || otherPath.isBlank()) {
            return this;
        } else {
            if (otherPath.isAbsolute()) {
                throw new IllegalArgumentException("otherPath can't be absolute");
            }
            return new DocPath(this.getParts(), otherPath.getParts());
        }
    }
Append otherPath onto the end of this and return a new {@link DocPath}
stroom-util-shared/src/main/java/stroom/util/shared/DocPath.java