Not with null, no.

Any line where you use length without properly checking if it is an array before.

One of the tested inputs is null. Your function needs to be able to handle it, but as you have it written now, the function fails because you try to find the length of null.

Read the error message: TypeError: Cannot read property 'length' of null it's not the length what is null, it's the value passed to your function, and null has no length.