code: public EntityBuilder addProperty(String name, Object value) {
      	if(StringUtils.isBlank(name)) {
      		throw new IllegalArgumentException("name cannot be null or empty.");
      	}
          addStep("_addProperty", new Object[] { name, value }, new Class<?>[]{String.class, Object.class}, true);
          return this;
      }
docs: Adds a single property to the entity to be built.
  Properties are optional according to the Siren specification.
  @param name cannot be <code>null</code> or empty.
  @param value may be <code>null</code> or empty.
  @return <code>this</code> builder, never <code>null</code>.