SSM中，前端搜索条件为空时，value为“”，传值时无法转换为int，会导致加载controller之前就报错，故应把属性值得类型改为Integer，即可接收到null
Field error in object 'xxx' on field 'XXX': rejected value [];
codes [typeMismatch.XXX.xxx,typeMismatch.xxx,typeMismatch.int,typeMismatch];
arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [XXX.xxx,xxx]; arguments [];
default message [xxx]];
default message [Failed to convert property value of type 'java.lang.String' to required type 'int' for property 'xxx'; nested exception is java.lang.NumberFormatException:
For input string: ""]