[assetslibrary] Add nullability to (generated and manual) bindings (#…

…14222)

Co-authored-by: TJ Lambert <[email protected]>

src/AssetsLibrary/ALAsset.cs

@@ -47,7 +47,7 @@ public double Duration {
 				// note: this can return an NSString like: ALErrorInvalidProperty
 				// which causes an InvalidCastException with a normal cast
 				var n = ValueForProperty (_PropertyDuration) as NSNumber;
-				return n == null ? double.NaN : n.DoubleValue;
+				return n?.DoubleValue ?? double.NaN;
 			}
 		}
 
@@ -81,9 +81,7 @@ public NSUrl? AssetUrl {
 			get {
 				// do not show an ArgumentNullException inside the
 				// debugger for releases before 6.0
-				if (_PropertyAssetURL == null)
-					return null;
-				return (NSUrl) ValueForProperty (_PropertyAssetURL);
+				return _PropertyAssetURL is not null ? (NSUrl) ValueForProperty (_PropertyAssetURL) : null;
 			}
 		}
 	}