[I] Dynamic log name using log4net.Util.PatternString giving null reference exception after update to 3.0.0 (logging-log4net)

[via GitHub]

Noahbambi1 opened a new issue, #186:
URL: https://github.com/apache/logging-log4net/issues/186

   Hi, 
   
   After updating to Log4net 3.0.0, i believe there is a bug in the config when 
using log4net.Util.PatternString to accept dynamic values for file names. 
   
   I have attached a zipped dotnet project that demonstrates the error.
   
[Log4NetExample.zip](https://github.com/user-attachments/files/17114068/Log4NetExample.zip)
   
   If the project is run as is, the null reference error will occur. 
   The line causing this error is in the log4net.config, where the logfile is 
specified as so:
   `<file type="log4net.Util.PatternString" value="Logs/%property{LogName}" />`
   
   In addition some code snippets below with context from the attached project. 
   
   When configuring a file name for storing logs here is the simple config:
   ```
   <?xml version="1.0" encoding="utf-8" ?>
   <log4net>
        <appender name="RollingFileAppender" 
type="log4net.Appender.RollingFileAppender">
                <file type="log4net.Util.PatternString" 
value="Logs/%property{LogName}" />
                <appendToFile value="true" />
                <rollingStyle value="Size" />
                <maxSizeRollBackups value="10" />
                <maximumFileSize value="10MB" />
                <staticLogFileName value="true" />
                <layout type="log4net.Layout.PatternLayout">
                        <conversionPattern value="%date [%thread] %-5level 
%logger - %message%newline" />
                </layout>
        </appender>
   
        <root>
                <level value="DEBUG" />
                <appender-ref ref="RollingFileAppender" />
        </root>
   </log4net>
   ```
   
   In this case the "Logname" is set in the program.cs of the project. 
   ```
   class Program
   {
       private static readonly ILog log = LogManager.GetLogger(typeof(Program));
   
       static void Main(string[] args)
       {
           // Load the log4net configuration
           var logRepository = 
LogManager.GetRepository(System.Reflection.Assembly.GetEntryAssembly());
           XmlConfigurator.Configure(logRepository, new 
FileInfo("log4net.config"));
   
           log4net.GlobalContext.Properties["LogName"] = "custom_log_" + 
DateTime.Now.ToString("yyyyMMdd_HHmmss");
           // Test logging
           log.Info("Application is starting.");
           log.Debug("This is a debug message.");
           log.Error("This is an error message.");
           log.Warn("This is a warning message.");
           log.Fatal("This is a fatal error message.");
   
           Console.WriteLine("Check the log file in the Logs folder.");
       }
   }
   ```
   
   With this setup, a null reference error occurs:
   
   ```
   log4net:WARN Unable to set property [file] on object 
[log4net.Appender.RollingFileAppender] using value [Logs/%property{LogName}] 
(with acceptable conversion types)
   log4net:ERROR Could not create Appender [RollingFileAppender] of type 
[log4net.Appender.RollingFileAppender]. Reported error follows.
   System.NullReferenceException: Object reference not set to an instance of an 
object.
      at log4net.Appender.RollingFileAppender.ActivateOptions()
      at 
log4net.Repository.Hierarchy.XmlHierarchyConfigurator.ParseAppender(XmlElement 
appenderElement)
   log4net:ERROR Appender named [RollingFileAppender] not found.
   ```
   
   


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