Created Issue: BindRound method binds nullable double as decimal [1580]

BindRound method binds nullable double as decimal.
```
private Expression BindRound(SingleValueFunctionCallNode node)
{
Contract.Assert("round" == node.Name);

Expression[] arguments = BindArguments(node.Parameters);

Contract.Assert(arguments.Length == 1 && IsDoubleOrDecimal(arguments[0].Type));

MethodInfo round = arguments[0].Type == typeof(double) ? ClrCanonicalFunctions.RoundOfDouble : ClrCanonicalFunctions.RoundOfDecimal;
return MakeFunctionCall(round, arguments);
}
```