Bug 190727 [regression]Default value issue when switch report parameter from textbox to listbox.[0705]
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
private boolean canBeBlank( )
	{
		boolean canBeBlank = false;
		if ( PARAM_CONTROL_LIST.equals( getSelectedControlType( ) )
				|| DesignChoiceConstants.PARAM_CONTROL_TEXT_BOX.equals( getSelectedControlType( ) ) )
		{
			if ( dirtyProperties.containsKey( CHECKBOX_ISREQUIRED ) )
			{
				canBeBlank = !( ( (Boolean) dirtyProperties.get( CHECKBOX_ISREQUIRED ) ).booleanValue( ) );
			}
			else
			{
				canBeBlank = !( inputParameter.isRequired( ) );
			}
		}
		return canBeBlank;
	}
	private boolean canBeNull( )
	{
		boolean canBeNull = false;
		if ( dirtyProperties.containsKey( CHECKBOX_ISREQUIRED ) )
		{
			canBeNull = !( ( (Boolean) dirtyProperties.get( CHECKBOX_ISREQUIRED ) ).booleanValue( ) );
		}
		else
		{
			canBeNull = !( inputParameter.isRequired( ) );
		}
		return canBeNull;
	}