Exception when formatting string

[maxbog]

This fails:

    [Test]
    public void ShouldFail()
    {
      // GIVEN
      var x1 = new List<string> { "aaa" };
      var x2 = new List<string> { "aaa" };

      XAssert.All(recorder => recorder.Equal(x1, x2));
    }

With this exception:

System.FormatException : Input string was not in a correct format.
   at System.Text.StringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ParamsArray args)
   at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args)
   at System.String.Format(String format, Object[] args)
   at FluentAssertions.Execution.AssertionScope.BecauseOf(String because, Object[] reasonArgs)
   at FluentAssertions.Primitives.ObjectAssertions.Be(Object expected, String because, Object[] reasonArgs)
   at BladTdd.Class1.ShouldFail() in Class1.cs: line 20