is to replace the null string in each element with the next element, resulting in a replacement string.
related codes
/ / the list array is as follows
var list = [
  "data : {null}", 
  "item : ( payload.data.list map(value0, index0) -> {null})",
  "gradeList : ( value0.gradeList map(value1, index1) -> {null})", 
  "otherList : ( value1.otherList map(value2, index2) -> {null})", 
  "anotherList : ( value2.anotherList map(value3, index3) -> {null})"
]
the desired result is a string
 "data : {
    item : ( payload.data.list map(value0, index0) -> {
        gradeList : ( value0.gradeList map(value1, index1) -> {
          otherList : ( value1.otherList map(value2, index2) -> {
            anotherList : ( value2.anotherList map(value3, index3) -> {null})
          })
        })
    })
  }"