JOLT Transform : Extract and combine fields from multiple JSON arrays to single array output, where one of the arrays can also be null

Question

I had asked a question previously: JOLT Transform : Extract and combine fields from multiple JSON arrays to single array output

This is a bit different question, where the arrays can actually consist null values.

Example 1:

{
  "questionResponses": [
    {
      "responses": null
    }
  ],
  "answers": [
    {
      "questionId": "1",
      "answerId": "answer 1"
    },
    {
      "questionId": "1",
      "answerId": "answer 2"
    }
  ],
  "totalAttachments": 0
}

Undesired Output:

null

Expected Output:

[
  {
    "response": null,
    "answerId": "answer 1"
  },
  {
    "response": null,
    "answerId": "answer 2"
  }
]

Example 2:

{
  "questionResponses": [
    {
      "responses": [
        {
          "responseId": "1",
          "response": "response 1"
        },
        {
          "responseId": "2",
          "response": "response 2"
        },
        {
          "responseId": "3",
          "response": "response 3"
        }
      ]
    }
  ],
  "answers": null,
  "totalAttachments": 0
}

Undesired Output:

null

Expected Output:

[
  {
    "response": "response 1",
    "answerId": null
  },
  {
    "response": "response 2",
    "answerId": null
  },
  {
    "response": "response 3",
    "answerId": null
  }
]

JOLT Spec:

[
  {
    "operation": "shift",
    "spec": {
      "questionR*": {
        "*": {
          "responses": {
            "*": {
              "@(4,answers)": "@(1,response)"
            }
          }
        }
      }
    }
  },
  {
    // Determine two independent arrays both with size of 6
    "operation": "shift",
    "spec": {
      "*": {
        "*": {
          "$1": "response",
          "a*": "&"
        }
      }
    }
  },
  {
    // expand those arrays as objects which contain desired key-value pairs
    "operation": "shift",
    "spec": {
      "*": {
        "*": "&.&1"
      }
    }
  },
  {
    // get rid of object labels
    "operation": "shift",
    "spec": {
      "*": ""
    }
  }
]

The JOLT Spec works as expected when both of the arrays consists at least single value. But fails when either of them is null.

Answer 1

You can use shift transformations to call responses and questionResponses individually while referencing one nested in another mutually, in first of them

(@(4,answers) nested within questionResponses

and

@(2,questionResponses) nested within answers)

such as

[
  {
    "operation": "shift",
    "spec": {
      "questionR*": {
        "*": {
          "responses": {
            "*": {
              "response": "[&1].&",
              "@(4,answers)": "[&1].answerId"
            }
          }
        }
      },
      "answers": {
        "*": {
          "@(2,questionResponses)": {
            "*": {
              "*": "&4.&.[&2]"
            }
          },
          "ans*": {
            "@": "&3.&1[&2]"
          }
        }
      }
    }
  },
  {
    "operation": "shift",
    "spec": {
      "answers": {
        "*": {
          "*": {
            "@": "[&].&2"
          }
        }
      },
      "*": ""
    }
  }
]

the demoes on the site http://jolt-demo.appspot.com/ :

for Example 1:

for Example 2: