Array destructuring - Ignoring some returned values - Error

[adros]

When I use array destructuring with ignored values, grasp throws error.
(see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment#Ignoring_some_returned_values)

echo 'var [a, , b] = f()' | grasp "*"
Cannot read property 'type' of null

I have checked also flow parser. It has no problems with parsing this code. The 'ignored value' is represented by NULL in elements array:

{
	"type": "ArrayPattern",
	"loc": {
		"source": null,
		"start": {
			"line": 1,
			"column": 4
		},
		"end": {
			"line": 1,
			"column": 12
		}
	},
	"range": [
		4,
		12
	],
	"elements": [
		{
			"type": "Identifier",
			"loc": {
				"source": null,
				"start": {
					"line": 1,
					"column": 5
				},
				"end": {
					"line": 1,
					"column": 6
				}
			},
			"range": [
				5,
				6
			],
			"name": "a",
			"typeAnnotation": null,
			"optional": false
		},
		null,
		{
			"type": "Identifier",
			"loc": {
				"source": null,
				"start": {
					"line": 1,
					"column": 10
				},
				"end": {
					"line": 1,
					"column": 11
				}
			},
			"range": [
				10,
				11
			],
			"name": "b",
			"typeAnnotation": null,
			"optional": false
		}
	],
	"typeAnnotation": null
},

[ainthek]

Please fix this, it fails in manu other scenarios:
echo 'const [, , , fieldName] = process.argv' | grasp -s 'program'
Cannot read property 'type' of null

[ainthek]

Acorn also emits null , see example:
$ echo 'const [, , , fieldName] = process.argv' | acorn
{
"type": "Program",
"start": 0,
"end": 39,
"body": [
{
"type": "VariableDeclaration",
"start": 0,
"end": 38,
"declarations": [
{
"type": "VariableDeclarator",
"start": 6,
"end": 38,
"id": {
"type": "ArrayPattern",
"start": 6,
"end": 23,
"elements": [
null,
null,
null,
{
"type": "Identifier",
"start": 13,
"end": 22,
"name": "fieldName"
}
]
},
"init": {
"type": "MemberExpression",
"start": 26,
"end": 38,
"object": {
"type": "Identifier",
"start": 26,
"end": 33,
"name": "process"
},
"property": {
"type": "Identifier",
"start": 34,
"end": 38,
"name": "argv"
},
"computed": false
}
}
],
"kind": "const"
}
],
"sourceType": "script"
}

[adros]

Works here: gratex@babd2bd