Sorry, but I think that your logic is wrong. How would you split this up:

3445space56space67
23space2space45
07spacespacespacespace

Does this mean that the columns for the last row should be 3? And if you are talking about NULL value - that would mean that the value simply does not exist and (in this case) the third row will have be:
07space06

Then how do you decide whether 06 is the second column or the third?