title: ArgumentNullException: Value cannot be null. Parameter name: constructor
body: <p>I'm building a ASP.NET 5 MVC application, using EF 7.
  I've got three models: 
  The Book class:</p>
  
  <pre><code>public class Book : IBook&lt;MangaChapter&gt;, IHasThumbnail, IBugChecker
      {
          public Book()
          {
              Chapters = new List&lt;MangaChapter&gt;();
          }
  
          [Key]
          public int ID { get; set; }
  
  
          [Required]
          public string Title { get; set; }
  
          [Required]
          [DataType(DataType.MultilineText)]
          public string Description { get; set; }
  
          public string ThumbnailPath { get; set; }
  
          public virtual IList&lt;Chapter&gt; Chapters { get; set; }
  }
  </code></pre>
  
  <p>The chapter class:</p>
  
  <pre><code>public class MangaChapter : IChapter&lt;MangaBook&gt;, IHasThumbnail
      {
          public MangaChapter()
          {
              PagesPath = new List&lt;Path&gt;();
          }
  
          [Key]
          public int ID { get; set; }
  
          [Required]
          public string Title { get; set; }
  
          public string ThumbnailPath { get; set; }
  
          public IList&lt;Path&gt; PagesPath { get; set; }
  
          public int BookID { get; set; }
          public MangaBook Book { get; set; }
      }
  }
  </code></pre>
  
  <p>and the path class, that I introduced just to store a list in EF</p>
  
  <pre><code>public class Path
      {
          public Path(string s) { P = s; }
  
          public int ID { get; set; }
  
          public string P { get; set; }
  
          public int MangaChapterID { get; set; }
  
          public MangaChapter MangaChapter { get; set; }
  
          public static implicit operator Path(string s)
          {
              return new Path(s);
          }
  
          public static implicit operator string(Path s)
          { return s.P; }
      }
  </code></pre>
  
  <p>the Problem is when I try to access the database using myDbContext, in this way:</p>
  
  <pre><code>var list = _db.Paths.ToList();
  </code></pre>
  
  <p>I get a Exception: ArgumentNullException: Value cannot be null.
   Parameter name: constructor.
  I've tried to access it in different ways, but always ended up with that exception.</p>
  
  <p>P.S.
  the source code for the application is entirely on  <a href="https://github.com/WizardOfMenlo/PolentaComics" rel="nofollow">GitHub</a></p>