DeleteProperty method 
    
    
  
Deletes the property from the bag.
The property to delete.
    
  Implementation
  void DeleteProperty(PropertyDefinition propertyDefinition) {
  if (!this._deletedProperties.containsKey(propertyDefinition)) {
    Object? propertyValue;
    propertyValue = this._properties[propertyDefinition];
    this._properties.remove(propertyDefinition);
    this._modifiedProperties.remove(propertyDefinition);
    this._deletedProperties[propertyDefinition] = propertyValue;
    if (propertyValue is ComplexProperty) {
      propertyValue.removeChangeEvent(this.PropertyChanged);
    }
  }
}