nazca #257026 Correctly check if index is not None rather than if index, as one can used the first column (index=0) for processing [validation pending]

prioritynormal
typebug
done in0.6.1
load0.100
load left0.000
closed by#d5dc8d2c4311 [distances] Correctly check if index is not None rather than if index, as one can used the first column (index=0) for processing, closes #257026