Null sql parameter value being passed as default

[Bruddles]

This if block is causing a null valued sql parameter to be passed to SQL as default.
When this parameter doesn't have a default, it throws a the exception:

The parameterized query '(@param decimal(5,2))select @param' expects the parameter '@param', which was not supplied.

CoreLibraries/Database/Schema/SqlProgramParameter.cs

Lines 160 to 164 in c172885

	if (value == null)
	{
	parameter.Value = null;
	return;
	}

[billings7]

Note: This has been fixed as part of the changes made for #45 and related issues, but that branch is not stable yet and contains a number of breaking changes.