SendPropertyChanged always null ?

[dba]

I'm having a problem with LINQ, I know my property isvalid is set to
true, when I step through the code it's fine, this._IsValid = value is
set to true, but when it gets to SendPropertyChanged it's always null.
The if is always false and never updates?

protected virtual void SendPropertyChanging()
{
if ((this.PropertyChanging != null))
{
this.PropertyChanging(this, emptyChangingEventArgs);
}
}

[Column(Storage="_IsValid", DbType="Bit")]
public System.Nullable<boolIsValid
{
get
{
return this._IsValid;
}
set
{
if ((this._IsValid != value))
{
this.OnIsValidChanging(value);
this.SendPropertyChanging();
this._IsValid = value;
this.SendPropertyChanged("IsValid");
this.OnIsValidChanged();
}
}
}