There are at least seven identifiers that convey nothingness in VBA:
Nothing is the starting value of an object variable before it has been initialized (or after it has been explicitly set to Nothing).
Null is a value that generally means "unknown." In VBA, only
Variant data types can hold a value of
Null. We use the
IsNull() function to test if a variable contains a null value.
Two double quotes on their own are used to represent a zero-length string.
vbNullString constant is similar to
"". The two can be used interchangeably in most situations.
The key difference is that
"" is a real string (meaning it occupies storage in memory) whereas
vbNullString is a "null string pointer." VBA treats it like a string, but it points to a memory address of zero (meaning it does not exist in memory).
Character with an ASCII code of zero. Equivalent to
This is the starting value of a
Variant variable before it has been assigned a value. Use the function
IsEmpty() to check for this value.
This is the value of an
Variant parameter when the calling code does not assign a value to the parameter. Use the function
IsMissing() to check for this value.
This article inspired by A Show About Nothing:
Cover image created with Microsoft Designer
UPDATE [2023-08-11]: Added brief mentions of the
IsMissing() functions that are used to check for
Missing values, respectively (h/t Colin Riddington).
UPDATE [2023-09-06]: Added links to deep dives on the following topics: Nothing, Null, Empty, and Missing.