Throws.Nothing doesn't work properly

[Michael Naumov]

The folowing Assert shouldn't fail but it fails

[Test]
public void NotThrown()
{
    Assert.That(() => null, Throws.Nothing);
}

NUnitBug.Tester.NotThrown:
System.ArgumentException : The actual value must be a TestDelegate
Parameter name: actual

at NUnit.Framework.Constraints.ThrowsNothingConstraint.Matches(Object actual)
at NUnit.Framework.Constraints.Constraint.Matches(ActualValueDelegate del)
at NUnitBug.Tester.NotThrown()

[Michael Naumov (mnaoumov)]

Tested on the latest version of NUnit: 2.5.8.10295

Due to source code it seems to be issue in the fact that
ThrowsNothingConstraint class doesn't override the following method from Constraint class

public virtual bool Matches(ActualValueDelegate del)
{
    return this.Matches(del());
}

it's should be overriden with

 public override bool Matches(ActualValueDelegate del)
    {
      TestDelegate actual = delegate {
        del();
      };
      return this.Matches(actual);
    }

(like in ThrowsConstraint class)