'Empty node2 value' error in normalize

[reveching]

In the tutorial notebook 'Analyzing CSKG', I got an error when i run '!kgtk normalize --verbose -i $PKG -o $TMPKG --columns-to-lower 'relation;dimension' source sentence 'node1;label' 'relation;label' 'node2;label'

The error says:
Empty node2 value when lowering 7 to 2: dimension in input line 1

even though I don't see any empty value in node2