code: public String getShortCommitId() {
  		String shortId = get("commit.id.abbrev");
  		if (shortId != null) {
  			return shortId;
  		}
  		String id = getCommitId();
  		if (id == null) {
  			return null;
  		}
  		return (id.length() > 7) ? id.substring(0, 7) : id;
  	}
docs: Return the abbreviated id of the commit or {@code null}.
  @return the short commit id