Ensure PerformanceBreakdown pieces cannot be null

osu.Game/Rulesets/Difficulty/PerformanceBreakdown.cs

@@ -1,8 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-#nullable disable
-
 namespace osu.Game.Rulesets.Difficulty
 {
     /// <summary>
@@ -19,5 +17,16 @@ namespace osu.Game.Rulesets.Difficulty
         /// Performance of a perfect play for comparison.
         /// </summary>
         public PerformanceAttributes PerfectPerformance { get; set; }
+
+        /// <summary>
+        /// Create a new performance breakdown.
+        /// </summary>
+        /// <param name="performance">Actual gameplay performance.</param>
+        /// <param name="perfectPerformance">Performance of a perfect play for comparison.</param>
+        public PerformanceBreakdown(PerformanceAttributes performance, PerformanceAttributes perfectPerformance)
+        {
+            Performance = performance;
+            PerfectPerformance = perfectPerformance;
+        }
     }
 }

osu.Game/Rulesets/Difficulty/PerformanceBreakdownCalculator.cs

@@ -40,7 +40,7 @@ namespace osu.Game.Rulesets.Difficulty
                 getPerfectPerformance(score, cancellationToken)
             ).ConfigureAwait(false);
 
-            return new PerformanceBreakdown { Performance = performanceArray[0], PerfectPerformance = performanceArray[1] };
+            return new PerformanceBreakdown(performanceArray[0] ?? new PerformanceAttributes(), performanceArray[1] ?? new PerformanceAttributes());
         }
 
         [ItemCanBeNull]