Don't throw ArgumentNullException in internal code

Nullable reference types are enabled on the project and TreatWarningsAsErrors is set to true. So this kind of error would be caught at compilation time.

This also allows to get rid of convoluted unit tests.

Author: 0xced

src/Log4NetTextFormatterOptions.cs

@@ -13,9 +13,9 @@ internal Log4NetTextFormatterOptions(IFormatProvider? formatProvider, CDataMode
             FormatProvider = formatProvider;
             CDataMode = cDataMode;
             Log4NetXmlNamespace = log4NetXmlNamespace;
-            XmlWriterSettings = xmlWriterSettings ?? throw new ArgumentNullException(nameof(xmlWriterSettings));
-            FilterProperty = filterProperty ?? throw new ArgumentNullException(nameof(filterProperty));
-            FormatException = formatException ?? throw new ArgumentNullException(nameof(formatException));
+            XmlWriterSettings = xmlWriterSettings;
+            FilterProperty = filterProperty;
+            FormatException = formatException;
         }
 
         /// See <see cref="Log4NetTextFormatterOptionsBuilder.FormatProvider"/>