groovy null list and empty list check

gistfile1.groovy

package io.geier

class IfTest {
    public static void main(String[] args) {
        List<String> emptyList = [];
        List<String> nullList = null;

        if (emptyList == null || emptyList.empty) {
            println "AAA emptyList"
        }

        if (emptyList?.empty) {
            println "BBB emptyList"
        }

        println "-----------------"

        if (nullList == null || nullList.empty) {
            println "AAA nullList"
        }

        if (nullList?.empty) {
            println "BBB nullList"
        }
    }
}

//
// OUTPUT:
// AAA emptyList
// BBB emptyList
// -----------------
// AAA nullList
//

Why not using groovy truth?
if(nullList){...}
if(emptyList){...}
?