Add converters

StabilityMatrix/Converters/NullToVisibilityConverter.cs

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+using System;
+using System.Globalization;
+using System.Windows;
+using System.Windows.Data;
+
+namespace StabilityMatrix.Converters;
+
+public class NullToVisibilityConverter : IValueConverter
+{
+    public object Convert(object? value, Type targetType, object parameter, CultureInfo culture)
+    {
+        return value == null ? Visibility.Collapsed : Visibility.Visible;
+    }
+
+    public object ConvertBack(object? value, Type targetType, object parameter, CultureInfo culture)
+    {
+        throw new NotImplementedException();
+    }
+}

StabilityMatrix/Converters/StringNullOrEmptyToVisibilityConverter.cs

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+using System;
+using System.Windows;
+using System.Windows.Data;
+
+namespace StabilityMatrix.Converters;
+
+public class StringNullOrEmptyToVisibilityConverter : IValueConverter
+{
+    public object Convert(object? value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
+    {
+        return string.IsNullOrEmpty(value as string) ? Visibility.Collapsed : Visibility.Visible;
+    }
+    public object? ConvertBack(object? value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
+    {
+        return null;
+    }
+}