Cannot delete parameter from Mistral action meta if only one parameter exists

[bmomberger-bitovi]

This appears to be a crawler error. When deleting parameters from Mistral workflows, the operation works as normal until deleting the last param. The following error is displayed in console:

crawler.js:158 Uncaught TypeError: Cannot set property 'prefix' of null
    at Object.replaceTokenValue (crawler.js:158)
    at Object.set (crawler.js:30)
    at MetaModel.set (base-class.js:94)
    at flowReducer (store.js:131)
    at reducer (store.js:383)
    at store.js:26
    at Array.forEach (<anonymous>)
    at rootReducer (store.js:26)
    at dispatch (createStore.js:178)
    at store.js:35

It appears that the crawler is not able to return a parent token with the value property properly set. When deleting not the last parameter, parentToken.value in crawler.replaceTokenValue() looks like:

{
  endPosition: 228
  jpath: (3) ["mappings", 2, "value"]
  kind: 2
  mappings: Array(2)
    0: {startPosition: 48, endPosition: 148, jpath: Array(5), range: Array(2), kind: 1, …}
    1: {startPosition: 148, endPosition: 228, jpath: Array(5), range: Array(2), kind: 1, …}
    length: 2
  range: Array(2)
    0: {row: 2, column: 10}
    1: {row: 13, column: 18}
    length: 2
  startPosition: 48
}

While when deleting the final one, parentToken.value gets created (via the factory creating a token from an empty object) to look like:

{
  endPosition: 0
  jpath: []
  kind: 2
  mappings: []
  range: Array(2)
    0: {row: 0, column: 0}
    1: {row: 0, column: 0}
  length: 2
  startPosition: 0
}

Without mappings there is no first value token (finding it returns null), so this sequence breaks:

        const newFirst = this.findFirstValueToken(parentToken.value);
        newFirst.prefix = oldFirst && oldFirst.prefix;

Either this operation should delete the key, or replacing the parent with an empty object should avoid attempting to set properties on the nonexistent new first value token.

I didn't look deep enough into this but I suspect that prefix here is for meaningful comments. Be careful not to break features that depend on the comments (placement and color) if fixing at the crawler level.

[bmomberger-bitovi]

Note, the code in crawler.js now looks like:

        const newFirst = this.findFirstValueToken(parentToken.value);
        if(oldFirst) {
          newFirst.prefix = oldFirst.prefix;
        }

Likely the correct fix is to do if(newFirst && oldFirst) {