Clean up

Author: MaggieKimani1

src/Microsoft.OpenApi/Reader/OpenApiJsonReader.cs

@@ -346,7 +346,7 @@ private async Task<ReadResult> ReadAsync(JsonNode jsonNode,
             };
         }
 
-        private void ResolveReferences(OpenApiDiagnostic diagnostic, OpenApiDocument document, OpenApiReaderSettings settings = null)
+        private void ResolveReferences(OpenApiDiagnostic diagnostic, OpenApiDocument document, OpenApiReaderSettings settings)
         {
             List<OpenApiError> errors = new();