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Also posted at: https://coderanch.com/t/681236/java/Imitating-file-system-Java-absolutely#3195319

Look at line 222 and find the variable on that line that has a null value.
Print all the variables on that line to see which one is null. Then backtrack in the code to find out why that variable...

Please copy the full text of the error message and paste it here. It has important info about the error.

The line number where the exception happened is shown in the error message. Look at that...