code: public AbstractRelationship getRelationship(final String id) {
  
  		if (id == null) {
  			return null;
  		}
  
  		final SecurityContext securityContext = getWebSocket().getSecurityContext();
  		final App app = StructrApp.getInstance(securityContext);
  
  		try (final Tx tx = app.tx()) {
  
  			final AbstractRelationship rel = (AbstractRelationship) app.getRelationshipById(id);
  
  			tx.success();
  
  			return rel;
  
  		} catch (FrameworkException fex) {
  			logger.warn("Unable to get relationship", fex);
  		}
  
  		return null;
  	}
docs: Returns the relationship to which the uuid parameter
  of this command refers to.
  
  @param id
  @return the node