converter fix

PacticeSolution/BindingValidationRuleSample/Converter/ButtonTextBrush.cs

@@ -15,10 +15,10 @@ namespace BindingValidationRuleSample.Converter
         public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
         {
             if (targetType != typeof(Brush))
-                return null;
+                return Brushes.Black;
 
             if (value == null)
-                return null;
+                return Brushes.Black;
 
             int age = int.Parse(value.ToString());
             return ValueColor(age);

PacticeSolution/BindingValidationRuleSample/MainWindow.xaml

@@ -38,7 +38,8 @@
         <TextBox Grid.Column="1" Grid.Row="0" Margin="5"
                  Text="{Binding Name, Mode=TwoWay}"/>
         <TextBox x:Name="tbxAge" Grid.Column="1" Grid.Row="1" Margin="5"
-                 ToolTip="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}">
+                 ToolTip="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"
+                 Foreground="{Binding Path=Age, Mode=TwoWay, Converter={StaticResource cvtAgeToBrush}}">
             <TextBox.Text>
                 <Binding Path="Age"
                          Mode="TwoWay"
@@ -49,8 +50,7 @@
                 </Binding>
             </TextBox.Text>
         </TextBox>
-        <TextBox Grid.Column="1" Grid.Row="2" Margin="5"
-                 Foreground="{Binding Path=Age, Mode=TwoWay, Converter={StaticResource cvtAgeToBrush}}"
+        <TextBox Grid.Column="1" Grid.Row="2" Margin="5" Foreground="Blue"
                  Text="{Binding PhoneNumber, Mode=TwoWay}"/>
 
         <Grid Grid.Column="0" Grid.Row="4" Grid.ColumnSpan="2" Height="30">