anchor.diff:        constructor Create(aValue: TDateTime); overload;
   
         procedure Assign(const aSource : TNullableDateTime); overload;
  -      procedure Assign(const aSourceField : TField); override; overload;
  +      procedure Assign(const aSourceField : TField); overload;
         procedure Assign (const aValue: Variant); override; overload;
  -      procedure Assign (const aValue: String); override; overload;
  +      procedure Assign (const aValue: String);  overload;
         function AsVariant: Variant; override;
         function CheckIfDifferentAndAssign(const aValue: Variant): boolean; override;
   
  
positive.code:   public
      constructor Create(); virtual;
      function AsVariant: Variant; virtual; abstract;
      procedure Assign(const aSourceField : TField); overload; virtual; abstract;
      procedure Assign (const aValue : String); overload; virtual; abstract;
      procedure Assign(const aValue: variant); overload; virtual; abstract;
  
      function CheckIfDifferentAndAssign(const aValue : Variant) : boolean; virtual; abstract;
  
negative.code:     constructor Create(aValue: Boolean); overload;
  
      procedure Assign(const aSource : TNullableBoolean); overload;
      procedure Assign(const aSourceField : TField); overload;
      procedure Assign(const aSourceField: TField; const aAllowNull: boolean); overload;
      procedure Assign (const aValue : Variant); override; overload;
      procedure Assign (const aValue : string); overload;
  
      function CheckIfDifferentAndAssign(const aValue : Variant) : boolean; override;
      function AsVariant: Variant; override;
  