We're glad that you managed to resolve your issue. Actually we were about to advise you the same thing - replace the values that shouldn't be shown with nulls. However, if in other scenarios you can't change your business object, you can apply a simple IIF
expression to the values on the Y axis, replacing the actual value with NULL
[Series.Y] = IIF(Fields.Y = 0, null, Fields.Y);
Please keep in mind that if your data contains points with valid Y values after the ones with NULL Y values, the graph processing engine will skip the NULL ones and just connect the two valid points. In this case we suggest you to prepare your data in advance, creating groups for non-null chunks of data and then create series group by that field. The idea is to divide the "valid" portions of your data and assign to each one of them a value that could be used to distinguish them later.
Hope it helps.