Handle issue with old .NET

CHANGELIST.md

@@ -29,6 +29,7 @@
 - Add flag for value being set
 - Add unused inputs to Aaru
 - Add self-formatting to Input types
+- Handle issue with old .NET
 
 ### 3.2.4 (2024-11-24)
 

MPF.ExecutionContexts/Data/BooleanInput.cs

@@ -50,7 +50,7 @@ namespace MPF.ExecutionContexts.Data
                 builder.Append(" ");
 
             // Value
-            builder.Append(Value.ToString().ToLowerInvariant());
+            builder.Append(Value.ToString()?.ToLowerInvariant());
 
             return builder.ToString();
         }