无法从BigDecimal强制转换为jasper中的String（奇怪的错误// $ JR_EXPR_ID = 18 $）

I have a jrxml file which has a field of BigDecimal value and when I try to execute the report. I get an error called " Cannot cast from BigDecimal to String in jasper". Im doing the report using ireport 5.6.0, and I get a weird error like this,I have a jrxml file which has a field of BigDec