Null values are stringified differently than string.Format

[chtenb]

Description
The documentation states that

Message templates are a superset of standard .NET format strings, so any format string acceptable to string.Format() will also be correctly processed by Serilog.

However, null values are printed by serilog as null but by string.Format as "". If this is intentional the docs should reflect this and my question becomes: how do I stringify null values as an empty string?

Reproduction

using Serilog;
using System.IO;

namespace ConsoleApp1 {
  class Program {
    static void Main(string[] args) {
      var logFileDir = @"path\to\dir";

      Log.Logger = new LoggerConfiguration().WriteTo.File(Path.Combine(logFileDir, "all.log")).CreateLogger();

      long? v = null;
      Log.Error("A long value {Value}.", v);
      Log.Information($"A long value {v}.");
      Log.CloseAndFlush();
    }
  }
}

The output is

2021-09-02 17:49:31.186 +02:00 [ERR] A long value null.
2021-09-02 17:49:31.206 +02:00 [INF] A long value .

Expected behavior

2021-09-02 17:49:31.186 +02:00 [ERR] A long value .
2021-09-02 17:49:31.206 +02:00 [INF] A long value .

Relevant package, tooling and runtime versions
Windows 10

  <package id="Serilog" version="2.10.0" targetFramework="net48" />
  <package id="Serilog.Sinks.File" version="5.0.0" targetFramework="net48" />

[nblumhardt]

Hi; thanks for the note. This is expected - the message template syntax is a superset of .NET format strings, but the formatting/substitution is not identical in all cases (this one, and arrays/enumerables, are the examples that come to mind).

You should be able to use an ILogEventEnricher to substitute nulls for empty strings if you want to (you may need to use WriteTo.Logger() if you want to apply the enricher to one sink only).

HTH!

[chtenb]

Is there any downside to having mixed types as value for a certain logevent property? In my case I'm logging a long?, but when I replace a null with "" the valuespace will be a mix of longs and strings.

[nblumhardt]

Will depend on the sink - it'll be fine for Console or File but may be less great when hooked up to log servers/databases

[nblumhardt]

Closing as I don't think there's much we can do here right now - but just to add to the above, in case it helps:

• You can do the enricher trick only on a sub-logger (WriteTo.Logger()) to control which sinks get nulls/empty strings switched, and
• Alternatively, you might find Serilog.Expressions's ExpressionTemplate has a more hackable formatting system which would allow (with some effort) a custom message() function to be plugged in in place of the built-in @m property that is responsible for rendering the message.

HTH!