#1683: fix NPE

[hohwille]

This PR fixes an NPE

that was reported in #1683 but the issue itself is about something else.

Implemented changes:

• fix NPE: make backup work also if IDE_HOME is undefined.

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Checklist for this PR

Make sure everything is checked before merging this PR. For further info please also see
our DoD.

• When running mvn clean test locally all tests pass and build is successful
• PR title is of the form #«issue-id»: «brief summary» (e.g. #921: fixed setup.bat). If no issue ID exists, title only.
• PR top-level comment summarizes what has been done and contains link to addressed issue(s)
• PR and issue(s) have suitable labels
• Issue is set to In Progress and assigned to you or there is no issue (might happen for very small PRs)
• You followed all coding conventions
• You have added the issue implemented by your PR in CHANGELOG.adoc unless issue is labeled
  with internal

[coveralls]

Pull Request Test Coverage Report for Build 21181339274

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 151 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.003%) to 70.454%

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Files with Coverage Reduction	New Missed Lines	%
com/devonfw/tools/ide/io/FileAccessImpl.java	151	67.4%

Totals
Change from base Build 21177469615:	-0.003%
Covered Lines:	10482
Relevant Lines:	14292

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💛 - Coveralls