VarIsNull

VarIsNull returns the boolean value of True if the variant variable or field V is null.

Null is still assigned, therefore this is different to an unassigned variant that is tested with the VarIsEmpty function VarIsEmpty.

Variant fields from Data Definitions will be initialised to null, and therefore you should use this function to test them.

Declaration: Function VarIsNull(const V : Variant) : Boolean;

An example of its use in mapping follows.

procedure OnMapEvent(var Value:Variant);
begin
  Value := VarIsNull(Field.Value)
end;

Other examples follow.

procedure ScriptEvent (var Value : variant);
var
  bVar : variant;
  ConfYN : boolean;
begin
  LogInfo('');
  ConfYN := VarIsNull(bVar);           //bVar is uninitialised so return is FALSE
  If ConfYN = True then
    LogInfo('The variant variable aVar is NULL')
  else
    LogInfo('The variant variable aVar is not NULL');
  LogInfo('');
 
  bVar := 'Hello campers!'
  ConfYN := VarIsNull(bVar);           //bVar is now initialised so return is FALSE
  If ConfYN = True then
    LogInfo('The variant variable aVar is still NULL')
  else
    LogInfo('The variant variable aVar is still not NULL');
  LogInfo('');
 
  bVar := null;                        //bVar is now NULL so return is TRUE
  ConfYN := VarIsNull(aVar);
  If ConfYN = True then
    LogInfo('The variant variable aVar is now NULL')
  else
    LogInfo('The variant variable aVar anything other than NULL');
  LogInfo('');
  
end;