Fixed: hide duplicate stacktrace for ModelState errors (#905)

* Fixed: hide stacktrace for ModelState errors

* Avoid to Demystify the same exception multiple times

Author: Bart Koelman

src/JsonApiDotNetCore/Errors/InvalidModelStateException.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Net;
 using System.Reflection;
@@ -80,7 +81,7 @@ private static Error FromModelError(ModelError modelError, string attributeName,
 
             if (includeExceptionStackTraceInErrors && modelError.Exception != null)
             {
-                error.Meta.IncludeExceptionStackTrace(modelError.Exception);
+                error.Meta.IncludeExceptionStackTrace(modelError.Exception.Demystify());
             }
 
             return error;

src/JsonApiDotNetCore/Middleware/ExceptionHandler.cs

@@ -99,7 +99,9 @@ protected virtual ErrorDocument CreateErrorDocument(Exception exception)
 
         private void ApplyOptions(Error error, Exception exception)
         {
-            error.Meta.IncludeExceptionStackTrace(_options.IncludeExceptionStackTraceInErrors ? exception : null);
+            Exception resultException = exception is InvalidModelStateException ? null : exception;
+
+            error.Meta.IncludeExceptionStackTrace(_options.IncludeExceptionStackTraceInErrors ? resultException : null);
         }
     }
 }

src/JsonApiDotNetCore/Serialization/Objects/ErrorMeta.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
 using Newtonsoft.Json;
 
 namespace JsonApiDotNetCore.Serialization.Objects
@@ -21,7 +20,7 @@ public void IncludeExceptionStackTrace(Exception exception)
             }
             else
             {
-                Data["StackTrace"] = exception.Demystify().ToString()
+                Data["StackTrace"] = exception.ToString()
                     .Split("\n", int.MaxValue, StringSplitOptions.RemoveEmptyEntries);
             }
         }