Merge pull request #347 from ozlerhakan/5.2.0

remove unusued classes

#348 add tests for records

Merge pull request #349 from Chelayel/feature/process_empty_cell

Merge branch '5.2.0' into feature/process_empty_cell

added additional unit test to combine processEmptyCell and preferNullOverDefault

changing how empty cells are handled, defaulting them to empty string, and adding unit tests

changing how empty cells are handled

added missing builder in PoijiOption and row handling in PoijiHandler

adding option to process empty cells

Bump version to 5.2.0 in README and pom.xml

Merge pull request #346 from Chelayel/joinbyname-nullpoiinter

adding null check on titleColumn

update versions in the docs

Merge pull request #344 from ozlerhakan/5.1.0