preprocess
Converts the given jdbcValue: J to a D.
If you intend to create a org.jetbrains.kotlinx.dataframe.columns.ColumnGroup, return a org.jetbrains.kotlinx.dataframe.DataRow here.
If you intend to create a org.jetbrains.kotlinx.dataframe.columns.FrameColumn, return a org.jetbrains.kotlinx.dataframe.DataFrame here.