Fix NPE in

[maheshacharya]

Here is the PR (#19) for NPE:
java.lang.NullPointerException
at com.smartsheet.tools.SmartsheetBackupService.backupOrgTo(SmartsheetBackupService.java:115)
at com.smartsheet.tools.SmartsheetBackupTool.main(SmartsheetBackupTool.java:107)