problem related to subreport in i-report with xpath

Question

if i use 1st expressino given bellow then master report shows sub report with null value at every place

1. ((net.sf.jasperreports.engine.data.JRXmlDataSource) $P{REPORT_DATA_SOURCE}).subDataSource(".")

and if i write 2nd expression starting from main the root node then it shows my sub report blank 2. ((net.sf.jasperreports.engine.data.JRXmlDataSource) $P{REPORT_DATA_SOURCE}).subDataSource("/main/adjustment/detail")

so how to solve this problem

i am using i report