Expression.Block behavior mismatch

This simple piece of code behaves differently if compiled under .Net Core and .Net Framework (I tested 4.7.2 only).

``` CSharp
Expression.Block(Array.Empty(), Array.Empty());
```

In detail, .Net Core works fine, while .Net Framework throws an exception complaining about the empty block.

Reading the documentation of [Expression.Block](https://docs.microsoft.com/en-us/dotnet/api/system.linq.expressions.expression.block?view=netframework-4.7.2) method, no exception is mentioned.

This breaks the contract and is a (bad) problem if you are writing a library that uses expressions to generate code on the fly.