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
}
	private void addCheckBoxListener( final Button checkBox, final String key )
	{
		checkBox.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{
				checkBoxChange( checkBox, key );
			}
		} );
	}
	/**
	 * @param key
	 * @param checkBox
	 * 
	 */
	protected void checkBoxChange( Button checkBox, String key )
	{
		dirtyProperties.put( key, new Boolean( checkBox.getSelection( ) ) );
		if ( CHECKBOX_ISREQUIRED.equals( key ) )
		{
			if ( isStatic( ) )
			{
				makeUniqueAndValid( );
				refreshValueTable( );
			}
			if ( getSelectedDataType( ).equals( DesignChoiceConstants.PARAM_TYPE_STRING ) )
			{
				clearDefaultValueChooser( checkBox.getSelection( ) );
			}
			updateMessageLine( );