Incomplete support of NullConditionalExpression in ExpressionEqualityComparer

[azabluda]

Since c9b5916#diff-5cd571c8981e88fd1f098652b72cf947R254 ExpressionEqualityComparer computes hash for NullConditionalExpression but still doesn't implement the comparison which leads to an exception.

Exception message: The method or operation is not implemented.

Stack trace:
System.NotImplementedException
The method or operation is not implemented.
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.ExpressionComparer.Compare(Expression a, Expression b)
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.ExpressionComparer.CompareBinary(BinaryExpression a, BinaryExpression b)
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.ExpressionComparer.CompareLambda(LambdaExpression a, LambdaExpression b)
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.ExpressionComparer.CompareExpressionList(IReadOnlyList`1 a, IReadOnlyList`1 b)
   at System.Collections.Generic.ObjectEqualityComparer`1.Equals(T x, T y)
   at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)
   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
   at Microsoft.Extensions.Caching.Memory.MemoryCache.TryGetValue(Object key, Object& result)
   at Microsoft.Extensions.Caching.Memory.CacheExtensions.TryGetValue[TItem](IMemoryCache cache, Object key, TItem& value)
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)

Steps to reproduce

Execute the query from the standard Null_conditional_simple test twice

[Fact]
public virtual void Null_conditional_simple_TWICE()
{
    var c = Expression.Parameter(typeof(Customer));

    var predicate
        = Expression.Lambda<Func<Customer, bool>>(
            Expression.Equal(
                new NullConditionalExpression(c, c, Expression.Property(c, "CustomerID")),
                Expression.Constant("ALFKI")),
            c);

    using (var dbContext = CreateContext())
    {
        var qry = dbContext.Customers.Where(predicate);
        qry.ToList(); // compile, cache and execute query [PASS]
        qry.ToList(); // fetch cached query and execute [FAIL]
    }
}

Further technical details

EF Core version: 1.1.0
Database Provider: InMemory
Operating system: Windows 7 Pro
IDE: Visual Studio 2015

[anpete]

Verified fixed.