check null value of property nested should be cast not nullable

[bigboss27051]

when I check null property in object in if scope I using that property in if scope null cast type to not nullable

if(object.firstname != null) {
String firstname = object.firstname;
}

this code error because object.firstname can nullable

[mateusfccp]

Fields are not promotable¹, for technical reasons.²

There's a label with many issues regarding this limitation, called field-promotion.

Currently, the two workarounds you have for this are:

final firstname = object.firstname; // Assignining to a local so it can be promoted

if (firstname != null) {
  // firstname is promoted here to non-nullable
}

if (object.firstname case final firstname?) {
  // firstname is introduced here as a non-nullable local
}

Footnotes

1. Private fields are promotable in some cases. See this issue. ↩

2. As far as I know, the main reason is because of field-getter symmetry. ↩

[lrhn]

Agree, this is the intended behavior, and while it's a known annoyance, there is no safe way to actually promote public non-local variables without constraining the author from making changes in the future.
For this to be allowed to work, the author of the class would have to have a way to opt in to promotion, like the stable getters (#1518) proposal.