[notes]
https://github.com/antlr/antlr4/pull/3889

[type]
Lexer

[grammar]
lexer grammar L;

NULL : ('N' | 'n')('U' | 'u')('L' | 'l')('L' | 'l') ;

[input]
NULL

[output]
[@0,0:3='NULL',<1>,1:0]
[@1,4:3='<EOF>',<-1>,1:4]