fix(BinarySearch): add null key check to prevent NPE (fix #7356)

[Senrian]

Fix Issue #7356

Problem

When key is null, key.compareTo(array[median]) throws NullPointerException.

Solution

Add early return of -1 when key == null.

if (key == null) {
    return -1;
}

---

由 OpenClaw 开源贡献助手自动提交

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.41%. Comparing base (cc75b5e) to head (091ef22).
⚠️ Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
.../java/com/thealgorithms/searches/BinarySearch.java	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7357      +/-   ##
============================================
- Coverage     79.45%   79.41%   -0.05%     
- Complexity     7083     7094      +11     
============================================
  Files           790      792       +2     
  Lines         23164    23226      +62     
  Branches       4556     4568      +12     
============================================
+ Hits          18405    18444      +39     
- Misses         4022     4046      +24     
+ Partials        737      736       -1     

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