Fix certain problems with expressions

- handle DefaultExpression when type is Void and cannot be instantiated
- To/FromSerializableForm for methods/members now supports non-public
  methods/members

Author: alex-kulakov

Orm/Xtensive.Orm/Core/Extensions/ExpressionExtensions.cs

@@ -135,7 +135,7 @@ public static ConstantExpression ToConstantExpression(this DefaultExpression def
     /// <returns>Object value of default value.</returns>
     public static object GetDefaultValue(this DefaultExpression defaultExpression)
     {
-      if (defaultExpression.Type.IsValueType) {
+      if (defaultExpression.Type != typeof(void) && defaultExpression.Type.IsValueType) {
         return StructDefaultValues.GetOrAdd<DefaultExpression>(
           defaultExpression.Type,
           (type, expr) => { return ((Func<object>) Expression.Lambda(Expression.Convert(expr, WellKnownTypes.Object)).Compile()).Invoke(); },

Orm/Xtensive.Orm/Linq/Internals/ExpressionHashCodeCalculator.cs

@@ -64,7 +64,7 @@ protected override int VisitConstant(ConstantExpression c)
     protected override int VisitDefault(DefaultExpression d)
     {
       if (d.Type.IsValueType) {
-        return d.GetDefaultValue().GetHashCode();
+        return d.GetDefaultValue()?.GetHashCode() ?? NullHashCode;
       }
       else {
         return NullHashCode;

Orm/Xtensive.Orm/Linq/SerializableExpressions/Internals/ReflectionExtensions.cs

@@ -30,7 +30,7 @@ public static string ToSerializableForm(this MethodInfo method)
         serializableName += method.ToString();
       else
         serializableName += method.GetGenericMethodDefinition() + Environment.NewLine +
-                            String.Join(Environment.NewLine,
+                            string.Join(Environment.NewLine,
                                         method.GetGenericArguments().Select(ty => ty.ToSerializableForm()).ToArray());
       return serializableName;
     }
@@ -42,7 +42,13 @@ public static MethodInfo GetMethodFromSerializableForm(this string serializedVal
 
       var fullName = SplitString(serializedValue);
       var name = fullName[1];
-      var method = Type.GetType(fullName[0]).GetMethods().First(m => m.ToString() == name);
+      var type = Type.GetType(fullName[0]);
+      var publicMethods = type.GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static);
+      var method = publicMethods.FirstOrDefault(m => m.ToString() == name);
+      if (method == null) {
+        var nonPublicMethods = type.GetMethods(BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static);
+        method = nonPublicMethods.First(m => m.ToString() == name);
+      }
 
       if (method.IsGenericMethod)
         method = method.MakeGenericMethod(fullName.Skip(2).Select(s => GetTypeFromSerializableForm(s)).ToArray());
@@ -64,7 +70,14 @@ public static MemberInfo GetMemberFromSerializableForm(this string serializedVal
 
       var fullName = SplitString(serializedValue);
       var name = fullName[1];
-      var member = Type.GetType(fullName[0]).GetMembers().First(m => m.ToString() == name);
+      var type = Type.GetType(fullName[0]);
+      var publicMemberss = type.GetMembers(BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static);
+      var member = publicMemberss.FirstOrDefault(m => m.ToString() == name);
+      if (member == null) {
+        var nonPublicMembers = type.GetMembers(BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static);
+        member = nonPublicMembers.First(m => m.ToString() == name);
+      }
+
       return member;
     }