Fix NullReferenceException in NpmLockfileDetectorBase when dependencies object is missing

[Copilot]

Summary

Fixed a NullReferenceException that occurred when processing package-lock.json files that don't contain a dependencies (v2) or packages (v3) object.

Root Cause

When a package-lock.json file is missing the dependencies or packages property, the ResolveDependencyObject() method returns null. The code then attempts to call .Children<JProperty>() on this null reference, causing a NullReferenceException:

var dependencies = this.ResolveDependencyObject(packageLockJToken); // Returns null
var dependencyLookup = dependencies.Children<JProperty>().ToDictionary(dependency => dependency.Name); // Throws

Solution

Added a null conditional operator with a fallback to an empty dictionary:

// Handle the case where dependencies is null (missing property in lockfile)
var dependencyLookup = dependencies?.Children<JProperty>().ToDictionary(dependency => dependency.Name) ?? [];

Testing

• Added comprehensive test cases for both lockfile v2 (dependencies) and v3 (packages) scenarios
• Created tests that reproduce the exact NullReferenceException condition
• Verified all 75 existing npm-related tests continue to pass
• Confirmed no regressions in functionality

Example

Before this fix, a package-lock.json file like this would crash:

{
  "name": "test",
  "version": "1.0.0",
  "lockfileVersion": 3
}

Now it processes gracefully without throwing an exception.

Fixes #1239.

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[jcfiorenzano]

@copilot try again

[jcfiorenzano]

@copilot try again

[github-actions]

👋 Hi! It looks like you modified some files in the Detectors folder.
You may need to bump the detector versions if any of the following scenarios apply:

• The detector detects more or fewer components than before
• The detector generates different parent/child graph relationships than before
• The detector generates different devDependencies values than before

If none of the above scenarios apply, feel free to ignore this comment 🙂

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.8%. Comparing base (adabadd) to head (4d1e858).

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #1437    +/-   ##
======================================
  Coverage   89.8%   89.8%            
======================================
  Files        414     414            
  Lines      32966   33078   +112     
  Branches    2045    2045            
======================================
+ Hits       29616   29731   +115     
+ Misses      2938    2934     -4     
- Partials     412     413     +1     

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