When using DVD Version Version 126.96.36.199.0-20190529084035
there is a difference in the handling of NULL values between the Preparation Tab and the Visualization Tap:
Within the Prepare Tab the NULL values are interpreted as empty strings, meaning if no Value is provided within the Source (e.g. a Database Table or an Excel Spreadsheet) then it is interpreted as a field with no content like ‘’, but not as a NULL value.
Below formula checks for NULL values using the IS NULL operator, but since null values are being interpreted as empty string, the evaluation is 1 for all values (of Payment date column):
when changing above formula from IS NULL check to a comparison of an empty string ‘’, the formula shows the below results were content is classified into 0 and 1:
The above figure shows the evaluation of the field by performing a check with an empty string ‘’. But, when switching from Prepare Tab to the Visualize Tab, the results do not coincide! The check for an empty string is not consistently evaluated, as shown below:
when using the empty string check on the Visualization Tab, every content of the Payment date field is evaluate to 1 (a value being present).
The Visualize Tab requires the IS NULL check to check for NULL values:
If you want to check for NULL values use the IS NULL or IS NOT NULL operator despite the results shown within the Prepare Tab. There are some Known Issues with the current version of DVD and the handling of null values as documented to some extend (the document is only in respect to Excel files, but above scenario is tested on Oracle Database) in this Known Issue document (from Sept ‘19).