title: Fluent NHibernate PersistenceSpecification can't test a collection of strings
body: <p>I'm using Fluent NHibernate to map a a class that has a collection of strings like this:</p>
  
  <pre><code>public class Foo {
      public virtual ICollection&lt;string&gt; Strings { get; set; }
  }
  public class FooMap : ClassMap&lt;Foo&gt; {
       public FooMap() { HasMany(f =&gt; f.Strings).Element("SomeColumnName"); }
  }
  </code></pre>
  
  <p>When I write a unit test using the <code>PersistenceSpecification</code> class included in the FNH package, it fails:</p>
  
  <pre><code>[TestMethod]
  public void CanMapCollectionOfStrings() {
      var someStrings = new List&lt;string&gt; { "Foo", "Bar", "Baz" };
      new PersistenceSpecification&lt;Foo&gt;(CurrentSession)
          .CheckList(x =&gt; x.Strings, someStrings) // MappingException
          .VerifyTheMappings();   
  }
  </code></pre>
  
  <p>This test throws <code>NHibernate.MappingException: No persister for: System.String</code> when calling <code>CheckList()</code>. However, if I try to persist the object myself, it works just fine.</p>
  
  <pre><code>[TestMethod]
  public void CanPersistCollectionOfStrings() {
      var foo = new Foo {
                       Strings = new List&lt;string&gt; { "Foo", "Bar", "Baz" };
                };
  
      CurrentSession.Save(foo);
      CurrentSession.Flush();
      var savedFoo = CurrentSession.Linq&lt;Foo&gt;.First();
      Assert.AreEqual(3, savedFoo.Strings.Count());
      // Test passes
  }
  </code></pre>
  
  <p>Why is the first unit test failing?</p>