Removed useless default values.

There's already an overload without the parameter.

src/Avalonia.Base/Data/BindingValue.cs

@@ -196,7 +196,7 @@ namespace Avalonia.Data
         /// </summary>
         /// <param name="defaultValue">The default value.</param>
         /// <returns>The value.</returns>
-        public T GetValueOrDefault(T defaultValue = default) => HasValue ? _value : defaultValue;
+        public T GetValueOrDefault(T defaultValue) => HasValue ? _value : defaultValue;
 
         /// <summary>
         /// Gets the value if present, otherwise the default value.
@@ -221,7 +221,7 @@ namespace Avalonia.Data
         /// present but not of the correct type or null, or <paramref name="defaultValue"/> if the
         /// value is not present.
         /// </returns>
-        public TResult GetValueOrDefault<TResult>(TResult defaultValue = default)
+        public TResult GetValueOrDefault<TResult>(TResult defaultValue)
         {
             return HasValue ?
                 _value is TResult result ? result : default

src/Avalonia.Base/Data/Optional.cs

@@ -76,7 +76,7 @@ namespace Avalonia.Data
         /// </summary>
         /// <param name="defaultValue">The default value.</param>
         /// <returns>The value.</returns>
-        public T GetValueOrDefault(T defaultValue = default) => HasValue ? _value : defaultValue;
+        public T GetValueOrDefault(T defaultValue) => HasValue ? _value : defaultValue;
 
         /// <summary>
         /// Gets the value if present, otherwise the default value.
@@ -101,7 +101,7 @@ namespace Avalonia.Data
         /// present but not of the correct type or null, or <paramref name="defaultValue"/> if the
         /// value is not present.
         /// </returns>
-        public TResult GetValueOrDefault<TResult>(TResult defaultValue = default)
+        public TResult GetValueOrDefault<TResult>(TResult defaultValue)
         {
             return HasValue ?
                 _value is TResult result ? result : default