If I don't do the flatmapelements method it performs as the java code. Only the flatmapelements produce errors.

Show us the stacktrace of the exception

Yes

You could try the following:

.via(SerializableFunction : { word: String -> word.split(" ") })

PCollection<String!>!

is it possible that

lines

contains `null`s?

no...

does it happen during the creation of

FlatMapElements

or when it is actually applied to

lines

?