How to start calculations from first non 0 / non empty value in Tableau

Question

I have a dataset on which I applied calculations to calculate the number of NULL values, the number of the maximum period with NULL values, etc...

I would like to adjust the calculations so the calculation start from the FIRST non 0 / non empty value

Also is it possible to have an additional calculation to add an extra column to display date of first and last date of non empty value?

Thank you for your help.

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Below are examples of expected values :

EAN A ,Result should still be 7 as after the first non NULL value(1 on 12/01) they are 7 NULL values

EAN C, the column number of _null days should return 0 in reality as there are no NULL values after the first non empty value (1 on the 12/9)

EAN G should be 0 as they are no NULL value after the first non-empty value (because there are no non-empty value)

For this calculation on Null days for example I would like to start it from the first non NULL value

WINDOW_SUM(SUM(IF [Value (full)]=0 THEN 1 ELSE 0 END))