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What is an elegant way to convert IDictionary<string, object> to IDictionary<string, string>

I have a method I am not happy with, can you please show me how to do this better.

public Foo WithBar(IDictionary<string, object> parameters) {
    var strStrDict = new Dictionary<string, string>(parameters.Count);
    foreach(var pair in parameters)
        strStrDict.Add(pair.Key, pair.Value != null ? pair.Value.ToString() : (string)null);
    // Call overload which takes IDictionary<string, string>  
    return this.WithBar(strStrDict);
This code works but I'm sure there is a nice linq'y way of doing this I am missing.
                One reason you should be unhappy with your method: It's broken! pair.Value == null ? pair.Value.ToString() : (string)null should blow up quite nicely.
– Anthony Pegram
                Apr 20, 2011 at 21:21
                Thanks Anthony, I asked the question and went off to write the unit test. So just found that.
– David Waters
                Apr 20, 2011 at 21:25
                @dykam, absolutely not. as performs a reference conversion, which will return null if the object is not a string. ToString returns a string representation of the object, which is something completely different...
– Thomas Levesque
                Apr 20, 2011 at 21:25
                Technically, (string)null is not required. In the expression condition ? obj.ToString() : null; the compiler has enough information to determine the type of the expression to be a string.
– Anthony Pegram
                Apr 20, 2011 at 21:27
                @Thomas Levesque, I assumed he had a Dict<string, object> where all keys where strings, so he just needed a cast. That still doesn't make asequivalent to your code indeed.
– Dykam
                Apr 21, 2011 at 9:23
                Convert.ToString(null) return String.Empty msdn.microsoft.com/en-us/library/astxcyeh.aspx, and failed my unit test :)
– David Waters
                Apr 20, 2011 at 21:33
                Interesting twist. In LinqPad (about to test in VS), Convert.ToString(null) returns null, but object obj = null; Convert.ToString(obj) returns empty string.
– Anthony Pegram
                Apr 20, 2011 at 21:38
                @David Waters I see :) I apparently tested against the wrong Convert.ToString (see updated answer). @Anthony Pegram Yeah, it takes the most "concrete" overload it can.
– Lasse Espeholt
                Apr 20, 2011 at 21:42
                yes, the documentation supports your edit. When passed null explicitly, overload resolution is picking the string version, which returns the string unchanged (hence getting null back). Since null works for object and string, overload resolution chooses the more specific type, which is string. Edit: Or what you just said.
– Anthony Pegram
                Apr 20, 2011 at 21:44
        
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