code: public static AtlasVertex addProperty(AtlasVertex vertex, String propertyName, Object value) {
          if (LOG.isDebugEnabled()) {
              LOG.debug("==> addProperty({}, {}, {})", toString(vertex), propertyName, value);
          }
          propertyName = encodePropertyKey(propertyName);
          vertex.addProperty(propertyName, value);
          return vertex;
      }
docs: Adds an additional value to a multi-property.
  
  @param propertyName
  @param value