VarIsNull

function VarIsNull(const V: Variant): Boolean;

VarIsNull returns true if the given variant contains the value Null. If the variant contains any other value, the function result is false.

Do not confuse a Null variant with an unassigned variant. A Null variant is still assigned, but has the value Null. Unlike unassigned variants, Null variants can be used in expressions and can be converted to other types of variants.

Example:

var
  valueInt : Integer;
  valueFlt : Float;
  valueStr : String;
  valueBool : Boolean;

begin

 valueInt := nil;
 if VarIsNull(valueInt) then
  ShowMessage('True');
 else
  ShowMessage('False');
  
 if VarIsNull(valueFlt) then
  ShowMessage('True');
 else
  ShowMessage('False');  
 
 if VarIsNull(valueStr) then
  ShowMessage('True');
 else
  ShowMessage('False');
  
 valueBool := true;
 if VarIsNull(valueBool) then
  ShowMessage('True');
 else
  ShowMessage('False');

end;

Output:

False
True
True
False