I realize that this is probably not the sort of thing you're looking for, but it's a handy thing to know about, and could help, if you are using SQL queries:

You can specify in the query what to return for a given field when the row being returned happens to have a null in that field. I don't know whether this is the sort of thing where the syntax varies from one database system to the next, but in Oracle, you would do something like this:

"select id,NVL(field_a,' '),NVL(field_b,'NO_B') from table..."
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The first arg to NVL() is a field to be returned, and the second arg is a string to be returned when the given field is null. It adds a bit of flexibility when doing queries, and can help simplify the perl scripting.