C# Building an Action Expression with a code block

I am tying to build an Expression tree that would represent this lamba:

Action<TFrom, TTo> map = 
    (from, to) => 
    {
        to.Property1 = (Nullable<TTo>)from.Property1;
        to.Property2 = (Nullable<TTo>)from.Property2;
        // ...continued for all properties
    };

Essentially, I am trying to map the non-nullable properties from one class to the Nullable properties of another class that share the same property name.

I have written this (incorrect) tree in my attempt to do this:

object i = new SomeObjWithOutNullable(); 
object j = new SomeObjWithNullable();

ParameterExpression p1 = Expression.Parameter(typeof(SomeObjWithOutNullable), "from");
ParameterExpression p2 = Expression.Parameter(typeof(SomeObjWithNullable), "to");

MemberExpression m1 = Expression.PropertyOrField(p1, "Property1");
MemberExpression m2 = Expression.PropertyOrField(p2, "Property1");
BinaryExpression body = Expression.Assign(m1, m2);
LambdaExpression lambda = Expression.Lambda<Action<SomeObjWithOutNullable,SomeObjWithNullable>>(body, new[] { p1,p2 });

var action = lambda.Compile();
action(i,j);

This does not compile. I get this exception when I attempt to: Edit:

Delegate 'System.Action<UserQuery.SomeObjWithOutNullable,UserQuery.SomeObjWithNullable>' has some invalid arguments
Argument 1: cannot convert from 'object' to 'UserQuery.SomeObjWithNullable'
Argument 2: cannot convert from 'object' to 'UserQuery.SomeObjWithNullable'

I know I have yet to add in the type conversion, but I cannot seem to figure out how to do even the assignment correctly. Any help would be appreciated.

Edit: Since I don't know what I am doing here, I have updated to a (i think) closer representation of the lambda I am trying to build