Transformer插件对于过滤数字类型字段值为null的无法过滤

想过滤数据库字段类型为int 值为null的字段 无法实现
`"transformer": [
{
"parameter": {
"columnIndex": 5,
"paras": [
"=",
"null"
]
},
"name": "dx_filter"
}`

上述这行代码，如果字段的值不为null 代码会往下走 走到FilterTransformer：225行会报错 因为过滤的参数值是 null

这行代码会报错 因为null不能转换为数字，应该是有bug 理论上如果过滤参数为null 是不是直接判断字段值为null 就直接过滤掉啊

Start at FilterTransformer line 225 and trace how the dx_filter transformer handles an integer column with a null filter parameter. Reproduce the issue with the configuration shown, then verify that filtering a null integer value no longer attempts to convert null to a number and that non-null values retain the expected behavior.

Written by the indexing model from the issue text.