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/CascadingParametersDialog.java
formatCategroy = formatPattern = null;
		}
		else
		{
			if ( !loading
					|| ( selectedParameter.getCategory( ) == null && selectedParameter.getPattern( ) == null ) )
			{
				if ( DesignChoiceConstants.PARAM_TYPE_STRING.equals( selectedDataType ) )
				{
					formatCategroy = choiceSet.findChoice( DesignChoiceConstants.STRING_FORMAT_TYPE_UNFORMATTED )
							.getName( );
				}
				else if ( DesignChoiceConstants.PARAM_TYPE_DATETIME.equals( selectedDataType ) )
				{
					formatCategroy = choiceSet.findChoice( DesignChoiceConstants.DATETIEM_FORMAT_TYPE_UNFORMATTED )
							.getName( );
				}
				else if ( DesignChoiceConstants.PARAM_TYPE_DECIMAL.equals( selectedDataType )
						|| DesignChoiceConstants.PARAM_TYPE_FLOAT.equals( selectedDataType )
						|| DesignChoiceConstants.PARAM_TYPE_INTEGER.equals( selectedDataType ) )
				{
					formatCategroy = choiceSet.findChoice( DesignChoiceConstants.NUMBER_FORMAT_TYPE_UNFORMATTED )
							.getName( );
				}
				formatPattern = null;
			}
			else
			{
				formatCategroy = selectedParameter.getCategory( );
				if ( formatCategroy == null )