The finer details of Meek's STV
In Meek STV, there is the concept of the quota or threshold that a candidate must exceed to be considered elected. This threshold is changed from round to round in the Meek STV system. The threshold changes based on how many votes are thrown away.

Let's say that your code is 4 5 6 and the rest blank, then once all those candidates are either elected or eliminated, the remaining part of your vote is considered "thrown away". Based on this, the threshold is changed for what candidates need to be elected in the next round.

In the STV system, the vote 0 2 4 0 1 6 is considered the same as 2 4 1 6 0 0, i.e. the zeros are automatically put at the end.

In the Stack Exchange moderator elections, it is possible to choose only a second candidate and a third candidate, but not a first. That is the same thing as choosing a first candidate and a second candidate.

Related on Meta Stack Exchange: How are moderator election votes counted, in pure English?