By the "billion dollar mistake", are you referring to null references [1]? But null references were introduced in 1965 in Algol, by Tony Hoare. They long predate Java.
I don't think it's about the existence of null references, but how Java is using them. Null references can be a useful, e.g. Kotlin has converted them to be useful (with nullable types).
Using nulls in Java is mostly a choice on the part of developers; even if you can't migrate to a JVM-targeted language like Scala, you can still adopt practices like null objects [0].