Update nested string field - elasticsearch

Question

I am trying to update a field image.uri by _update_by_query:
POST user/_update_by_query
{
"script": {
"source": "ctx._source.image.uri = 'https://example.com/default/image/profile.jpg'",
"lang": "painless"
},
"query": {
"bool": {
"must_not": [
{
"exists": {
"field": "image.id"
}
}
]
}
}
}
But it throws error:
{
"error": {
"root_cause": [
{
"type": "script_exception",
"reason": "runtime error",
"script_stack": [
"ctx._source.image.uri = 'https://example.com/default/image/profile.jpg'",
" ^---- HERE"
],
"script": "ctx._source.image.uri = 'https://example.com/default/image/profile.jpg'",
"lang": "painless"
}
],
"type": "script_exception",
"reason": "runtime error",
"script_stack": [
"ctx._source.image.uri = 'https://example.com/default/image/profile.jpg'",
" ^---- HERE"
],
"script": "ctx._source.image.uri = 'https://example.com/default/image/profile.jpg'",
"lang": "painless",
"caused_by": {
"type": "null_pointer_exception",
"reason": null
}
},
"status": 500
}
A sample document:
{
"image": {
"uri": "https://example.com/resources/uploads/default_files/profile/thumb/large/default_profile.jpg"
},
"created": "2018-06-06T21:49:26Z",
"uid": 1,
"name": "Jason Cameron",
"username": "jason"
}

Answer 1

UPDATED RESPONE
The problem could be coming from a document without image object in it.
Try to add strict mapping if possible, to avoid indexing documents without image object.
OLD RESPONSE/"\' are correct for use inside painless script as string
Your problem comes as use of ' to encapsulate your uri, strings must be encapsulated by ".
Try to modify your script as:
"script": {
"source": "ctx._source.image.uri = \"https://example.com/default/image/profile.jpg\"",
"lang": "painless"
}