Controlling Nulls
One of the common bugaboos that haunt novice Access programmers is working with null values. When a field or variable is Null, it signifies that it has no valid data. This is in contrast to zero-length, which means that the value contains a string that has a zero length, or Empty, which means that a variant variable has not been initialized (assigned a value for the first time). All three values are hard to distinguish because they all represent a non or blank value. To help you differentiate between the three, keep the following in mind:
Variant is the only data type that can hold the Empty, Null, and Nothing special values.
The Null, Empty, and zero-length values all have no character that outputs to either a screen or a printer. ...
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