Bug 182673 No default value error message prompts incorrectly
Steps to reproduce: 1. New a report parameter; 2. Choose control type as Combo; 3. Choose parameter as dynamic type; Expected result: As the isRequired is false by default, parameter's default value can be null value. There should be no error message about no default value prompt. Actual result; Error messages prompts
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
}
			} );
			if ( dialog.open( ) == Dialog.OK )
			{
				choice.setValue( convertToStandardFormat( choice.getValue( ) ) );
				choiceList.add( choice );
				return true;
			}
			return false;
		}
		public boolean removeItem( Object[] elements )
		{
			for ( int i = 0; i < elements.length; i++ )
			{
				if ( isDefaultChoice( (SelectionChoice) elements[i] ) )
				{
					changeDefaultValue( null );
				}
				choiceList.remove( elements[i] );
			}
			return true;
		}
	};
	private Text listLimit;
	/**
	 * Create a new parameter dialog with given title under the active shell
	 * 
	 * @param title
	 *            the title of the dialog
	 */