Fix or disable multiple warnings

src/DesktopMagicPluginAPI/Drawing/FontComparer.cs

@@ -6,8 +6,13 @@ namespace DesktopMagic.Api.Drawing;
 
 internal class FontComparer : IEqualityComparer<Font>
 {
-    public bool Equals(Font font1, Font font2)
+    public bool Equals(Font? font1, Font? font2)
     {
+        if (font1 is null || font2 is null)
+        {
+            return false;
+        }
+
         if (font1.Name != font2.Name)
         {
             return false;

src/DesktopMagicPluginAPI/Settings/Button.cs

@@ -10,9 +10,9 @@ public class Button : Setting
     /// <summary>
     /// Occurs when the button gets clicked.
     /// </summary>
-    public event Action OnClick;
+    public event Action? OnClick;
 
-    private string _value;
+    private string _value = string.Empty;
 
     /// <summary>
     /// Gets or sets the text caption displayed in the <see cref="Button"/> element.

src/DesktopMagicPluginAPI/Settings/Label.cs

@@ -5,7 +5,7 @@
 /// </summary>
 public class Label : Setting
 {
-    private string _value;
+    private string _value = string.Empty;
 
     /// <summary>
     /// Gets or sets the text associated with this <see cref="Label"/>.

src/DesktopMagicPluginAPI/Settings/TextBox.cs

@@ -5,7 +5,7 @@
 /// </summary>
 public class TextBox : Setting
 {
-    private string _value;
+    private string _value = string.Empty;
 
     /// <summary>
     /// Gets or sets the text associated with this <see cref="TextBox"/>.