fix: defensive programming has been added to api 'GetEntries()' to reduce NPE

[zong-zhe]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

Fixed #228

2. What is the scope of this PR (e.g. component or file name):

Defensive programming has been added to api 'GetEntries()' to reduce NPE

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

[coveralls]

Pull Request Test Coverage Report for Build 7320132587

• 1 of 4 (25.0%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.1%) to 39.835%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/package/modfile.go	0	1	0.0%
pkg/package/package.go	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
pkg/package/package.go	1	39.84%

Totals
Change from base Build 7319653945:	0.1%
Covered Lines:	1495
Relevant Lines:	3753

---

💛 - Coveralls

[Peefy]

LGTM