code: public OSchemaHelper linkedClass(String className)
  	{
  		checkOProperty();
  		OClass linkedToClass =  schema.getClass(className);
  		if(linkedToClass==null) throw new IllegalArgumentException("Target OClass '"+className+"' to link to not found");
  		if(!Objects.equal(linkedToClass, lastProperty.getLinkedClass()))
  		{
  			lastProperty.setLinkedClass(linkedToClass);
  		}
  		return this;
  	}
docs: Set linked class to a current property
  @param className class name to set as a linked class
  @return this helper