Pentaho Kettle Failed to parse Number: For input string: "null" error

I am new to Pentaho Kettle and I am trying to read simple data (.DBF file) with Xbase. But I keep getting errors when reading my DBF data file

The error is:

... Unable to read row from XBase file; Failed to parse Number: For input string: "null";Caused by: com.linuxense.javadbf.DBFException: Failed to parse Number: For input string: "null"

What does this mean exactly and how do I handle it?

Thank you in advance