IS null safety compulsory in Flutter?

Migrating to null safety

There are many reasons to migrate Flutter apps to null safety, like those mentioned above, and it’s a must-do . This feature is a breaking change and previously written apps will not compile with the null checker on which might tempt some lazy developers to not activate it.23 Mar 2021

For us, in the context of null safety, that means that if an expression has a static type that does not permit null , then no possible execution of that expression can ever evaluate to null . The language provides this guarantee mostly through static checks, but there can be some runtime checks involved too.