Hi Both,
how about using the Column Auto Type Cast for this:
You can define a Missing Value pattern in the dialog. If you do this, it will automatically transform all emptys to Missing Values (And as a nice Side Effect the columns are automatically converted to the best fitting type)
https://hub.knime.com/knime/nodes/Column_Auto_Type_Cast*iQCmMxBEl2szprD5
Cheers, Iris