presto-main/src/main/java/io/prestosql/sql/gen/JoinCompiler.java/JoinCompiler/typeHashCode
class JoinCompiler:    private static BytecodeNode typeHashCode(BytecodeExpression type, BytecodeExpression blockRef, BytecodeExpression blockPosition)
    {
        return new IfStatement()
                .condition(blockRef.invoke("isNull", boolean.class, blockPosition))
                .ifTrue(constantLong(0L))
                .ifFalse(type.invoke("hash", long.class, blockRef, blockPosition));
    }