defined-or "//" over multiple lines

Question

Why are version 1,2 and 3 working, but version 4 fails with: Null regex not allowed when using // over multiple lines?

#1
say Nil         //
    try {'a'++} //
    1;

#2
say    Nil
    // try {'a'++} //
       2;

#3
say   Nil
   // 3;

#Fails with: Null regex not allowed
say        Nil
        // try {'a'++}
        // 4;

Answer 1

There is try block at the end of a line. It is same as

say        Nil
    // try {'a'++};
    // 4;

See documentation: It is OK to skip the semicolon between the last statement in a block and the closing }.

You can try

say        Nil
    // try {'a'++}\
    // 4;

or

say        Nil
    // (try {'a'++})
    // 4;