Range returning null using getRange

I am new to Google Apps Script and the docs are a little fuzzy on the returned data from a method call. I want to loop through a range, but it is coming back as null. What am I doing wrong?

var currentSheet = SpreadsheetApp.getActiveSheet();var loopRng = currentSheet.getRange('B4:B34');var counter = 0;Logger.log(loopRng.length);for(var i = 0; i < loopRng.length; i++) { counter++; Logger.log(counter);}}