结构调整，便于后续扩展

AIStudio.Wpf.BaseDiagram/Converters/NullableToBooleanConverter.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Globalization;
+using System.Windows;
+using System.Windows.Data;
+
+namespace AIStudio.Wpf.BaseDiagram.Converters
+{
+    public class NullableToBooleanConverter : IValueConverter
+    {
+        public bool NullValue { get; set; } = false;
+        public bool NotNullValue { get; set; } = true;
+
+        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            return value == null ? NullValue : NotNullValue;
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            return Binding.DoNothing;
+        }
+    }
+}