Merge pull request #516 from User00015/NullableInclude

Include/IncludeMany on nullable FK no longer throws exception.

Author: ahmad-moussawi

SqlKata.Execution/QueryFactory.cs

@@ -749,8 +749,8 @@ private static IEnumerable<T> handleIncludes<T>(Query query, IEnumerable<T> resu
 
                 foreach (var item in dynamicResult)
                 {
-                    var foreignValue = item[include.ForeignKey].ToString();
-                    item[include.Name] = related.ContainsKey(foreignValue) ? related[foreignValue] : null;
+                    var foreignValue = item[include.ForeignKey]?.ToString();
+                    item[include.Name] = foreignValue != null && related.ContainsKey(foreignValue) ? related[foreignValue] : null;
                 }
             }
 
@@ -843,8 +843,8 @@ private static async Task<IEnumerable<T>> handleIncludesAsync<T>(Query query, IE
 
                 foreach (var item in dynamicResult)
                 {
-                    var foreignValue = item[include.ForeignKey].ToString();
-                    item[include.Name] = related.ContainsKey(foreignValue) ? related[foreignValue] : null;
+                    var foreignValue = item[include.ForeignKey]?.ToString();
+                    item[include.Name] = foreignValue != null && related.ContainsKey(foreignValue) ? related[foreignValue] : null;
                 }
             }