Add support for 'HasValue' and 'Value' for properties of type `Nullable<T>`

[carusology]

Background

If you attempt to use the HasValue or Value on a queryable's property that is an instance of Nullable<T> within a LINQ expression, you will get an exception with the message "The member '[Has]Value' is not supported".

Here's an example.

Given the following data model...

public class Fake : ImmutableBase<Fake> {

    public Nullable<DateTime> OptionalDate { get; }

    public Fake(Nullable<DateTime> optionalDate = null) {
        this.OptionalDate = optionalDate;
    }
}

... this code will throw exceptions with the aforementioned message.

IQueryable<Fake> queryable = ...;

var nonNullDates = 
    queryable
        .Where(model => model.OptionalDate.HasValue)
        .Select(model => model.OptionalDate.Value)
        .ToImmutableList();

Task

Add support for HasValue and Value for properties of type Nullable<TValueType> that exist on a class being queried via a FSharp.MySqlQueryProvider. Presumably "HasValue" property should be converted to a MySQL-based "IS NULL" check, and "Value" property should be a ignored / passed through.

Stack Trace

Error Message:
 System.Exception : The member 'HasValue' is not supported
Stack Trace:
   at FSharp.MySqlQueryProvider.QueryTranslator.result@807-5.Invoke(String message)
   at FSharp.MySqlQueryProvider.QueryTranslator.mapFun@306-2.Invoke(Expression e)
   at FSharp.MySqlQueryProvider.Expression.visitor@45.Invoke(Expression e)
   at FSharp.MySqlQueryProvider.Expression.Visitor.Visit(Expression expression)
   at FSharp.MySqlQueryProvider.Expression.map[t](FSharpFunc`2 mapping, Expression expression)
   at FSharp.MySqlQueryProvider.QueryTranslator.fromWhere@575.Invoke(MethodCallExpression w)
   at Microsoft.FSharp.Primitives.Basics.List.map[T,TResult](FSharpFunc`2 mapping, FSharpList`1 x)
   at FSharp.MySqlQueryProvider.QueryTranslator.mapFun@306-2.Invoke(Expression e)
   at FSharp.MySqlQueryProvider.Expression.visitor@45.Invoke(Expression e)
   at FSharp.MySqlQueryProvider.Expression.Visitor.Visit(Expression expression)
   at FSharp.MySqlQueryProvider.Expression.map[t](FSharpFunc`2 mapping, Expression expression)
   at FSharp.MySqlQueryProvider.QueryTranslator.translate(QueryDialect _queryDialect, QueryType queryType, FSharpOption`1 getDBType, FSharpOption`1 getTableName, FSharpOption`1 getColumnName, Expression expression)
   at FSharp.MySqlQueryProvider.QueryTranslator.translateToCommand(QueryDialect queryDialect, QueryType queryType, FSharpOption`1 getDBType, FSharpOption`1 getTableName, FSharpOption`1 getColumnName, MySqlConnection connection, Expression expression)
   at FSharp.MySqlQueryProvider.MySqlQueryProvider.translate(MySqlConnection con, Expression expression)
   at FSharp.MySqlQueryProvider.MySqlQueryProvider.Execute(Expression expression)
   at FSharp.MySqlQueryProvider.Queryable.f@1[T](Query`1 this, Unit unitVar0)
   at FSharp.MySqlQueryProvider.Queryable.Query`1.getEnumerable()
   at FSharp.MySqlQueryProvider.Queryable.Query`1.System-Collections-Generic-IEnumerable`1-GetEnumerator()