get default series of JE via DI API

I want default series of JE Using DI API

I tried to get Default series Using Query given below

String.Format("select NextNumber,isnull(LastNum ,-1 ) LastNum from nnm1 where series = '{0}' AND ObjectCode = '30'", je.Series)

but it gives no result

can Anyone Know about this .

regards

Salman Nazir