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:

Base Syntax

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;

TRObject Syntax

 var
   valueInt : Integer;
   valueFlt : Float;
   valueStr : String;
   valueBool : Boolean;
 
 {
 
  valueInt = nil;
  if (VarIsNull(valueInt))
   ShowMessage('True');
  else
   ShowMessage('False');
   
  if (VarIsNull(valueFlt))
   ShowMessage('True');
  else
   ShowMessage('False');  
  
  if (VarIsNull(valueStr))
   ShowMessage('True');
  else
   ShowMessage('False');
   
  valueBool = true;
  if (VarIsNull(valueBool))
   ShowMessage('True');
  else
   ShowMessage('False');
 
 }

Output:

False
True
True
False