coalesce

Returns the first value from the given arguments that is non-null. For example, given a record such as:

{
  "id": null,
  "name": "John Doe"
}

The following record path would return "John Doe":

coalesce(/id, /name)

Given the record:

{
  "id": "1234",
  "name": null
}

The same record path would return "1234".

Given the record:

{
  "id": null,
  "name": null
}

The record path would return null.

Given the record:

{
  "id": "null",
  "name": "John Doe"
}

The record path would return the String "null". Note here the very important difference in that the id field does not have a null value but rather the value of the field is the literal string "null".

Given the record:

{
  "name": null
}

The record path would return null. Given that the id field is not present, it is treated as a null value.

Given the record:

{
  "id": "1234",
  "name": "John Doe"
}

The record path would return "1234". However, the record path coalesce(/name, /id) would return "John Doe" because both fields given are non-null, so the coalesce function returns the first value that is referenced in its arguments, not the first value that is encountered in the Record itself.