Thank you for your answer. Unfortunately I was unable to get it working. The if never triggered.
I managed to get the following working:
if str(Col1Dat[i]) == "NaN":
I understand that this is not elegant but I was unable to find out what is stored in those items that have NULL value returns from the SQL call, however it seems stable to convert whatever is stored to a string and compare with “Nan”, which I presume stands for “Not a Number”.
I guess there are some who wonder why I do this at all. The reason is that I have several (thousands) of different time series data that I want to be able to study and compare using Table, Chart and Bar Chart components. Unfortunately there are gaps in my data due to the fact that equipment is shut down or otherwise off line from time to time. In order to compare the information I need to fill out the gaps so that all samples are represented. Carl devised a way to get the SQL server to fill in for me using a separate table containing only sampling instances and joining. This works perfectly and results in missing samples being represented by NULL values (whatever they are) from the database. Those NULL:s show up as rectangles in the Table component which is OK. I have not had time to study the Chart component behaviour but I noticed that the Bar Chart component fails miserably when fed NULL values so I need to exchange them for something that the component can accept.
Sorry for the loooong post!