code: public ObjectSchema withRequiredProperty(String name, Object type, IValidationRule... rules) {
  		_properties = _properties != null ? _properties : new ArrayList<PropertySchema>();
  		PropertySchema schema = new PropertySchema(name, type);
  		schema.setRules(Arrays.asList(rules));
  		schema.makeRequired();
  		return withProperty(schema);
  	}
docs: Adds a validation schema for a required object property.
  
  @param name  a property name.
  @param type  (optional) a property schema or type.
  @param rules (optional) a list of property validation rules.
  @return the validation schema