请教各位：struts2 自带 json插件报错java.lang.NoSuchMethodException: com.bx.cloud.bs.vo.ps.PsUser.getCallbacks()

请教:struts2自带json插件报错Java . lang . nosuchmethodexception:com . bx . cloud . bs . VO . PS . psuser . get callbacks()请教:struts2自带json插件报错Java . lang . nosuchmethodexception:com . bx . cloud . bs . VO . PS . psuser . get callbacks()简介:报错信息如下:Java . lang . nullpointerexception at org . Apache . struts 2 . JSON . JSON writer . findbase accessor