The following is the problem query.

MetricValue nvarchar(50)
Valid values for TargetValue can be NULL, '', or some other string.

INSERT INTO @M (ParameterID, EntityID, TargetValue)
SELECT M.ParameterID, M.EntityID, M.MetricValue
    FROM tblMetric M
    INNER JOIN @ins i ON M.ParameterID = i.ParameterID AND M.EntityID =
i.EntityID
    INNER JOIN (SELECT ParameterID, EntityID, MetricDate AS TargetDate,
MetricValue AS TargetValue
                    FROM tblMetric
                WHERE MetricTypeID = @TargTypeID) TM ON i.EntityID = TM.EntityID AND
i.ParameterID = TM.ParameterID AND i.TargetDate = TM.TargetDate
WHERE MetricTypeID IN (@BaseTypeID, @MonTypeID)

The problem is that when it is Null, @M.TargetValue ends up being ''.  How
can I avoid this?