Fix the issue that a NullPointerException occurs when initialize the unified configuration

[hanbingleixue]

What type of PR is this?

Bug

What this PR does / why we need it?

Fix the issue that a NullPointerException occurs when the configuration item type is set and the configuration content is empty during configuration initialization parsing. When the configuration type of a configuration item is collection and the configuration content is empty, an warning log is recorded. The LogEventCollector collects and reports warning logs. However, the event configuration is not initialized, so a NullPointerException is thrown on event collection

Which issue(s) this PR fixes？

Fixes #1591

Does this PR introduce a user-facing change?

No

Checklist

• Make sure there is a GitHub_issue related with this PR before you start working on it.
• Make sure you have squashed your change to one single commit.
• GitHub Actions works fine in this PR.

[codecov]

Codecov Report

Attention: Patch coverage is 9.09091% with 10 lines in your changes missing coverage. Please review.

Files	Patch %	Lines
.../io/sermant/core/config/utils/ConfigValueUtil.java	0.00%	4 Missing ⚠️
...ain/java/io/sermant/core/event/EventCollector.java	20.00%	4 Missing ⚠️
...ermant/core/event/collector/LogEventCollector.java	0.00%	2 Missing ⚠️

Flag	Coverage Δ	Complexity Δ
unittests	43.02% <9.09%> (+0.03%)	182.00 <0.00> (+1.00)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ	Complexity Δ
.../core/event/collector/FrameworkEventCollector.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...mant/router/common/event/RouterEventCollector.java	25.64% <ø> (-5.32%)	0.00 <0.00> (ø)
...covery/event/SpringBootRegistryEventCollector.java	22.58% <ø> (-6.84%)	0.00 <0.00> (ø)
...ermant/core/event/collector/LogEventCollector.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
.../io/sermant/core/config/utils/ConfigValueUtil.java	40.45% <0.00%> (-1.28%)	0.00 <0.00> (ø)
...ain/java/io/sermant/core/event/EventCollector.java	15.00% <20.00%> (-1.22%)	0.00 <0.00> (ø)

... and 25 files with indirect coverage changes