fix NullPointerException hazard in StringUtils.join(..) method

[WillardHu]

Signed-off-by: WillardHu [email protected]

What's the purpose of this PR

When the collection is null, a NullPointerException is thrown here. Otherwise iterator == null is always false.

Which issue(s) this PR fixes:

Fixes #

Brief changelog

fix NullPointerException hazard in StringUtils.join(..) method.

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[codecov-commenter]

Codecov Report

Merging #3983 (9e30ebe) into master (0b5d227) will increase coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #3983   +/-   ##
=========================================
  Coverage     50.76%   50.76%           
+ Complexity     2468     2462    -6     
=========================================
  Files           475      475           
  Lines         14600    14580   -20     
  Branches       1521     1514    -7     
=========================================
- Hits           7412     7402   -10     
+ Misses         6661     6651   -10     
  Partials        527      527           

Impacted Files	Coverage Δ
...ctrip/framework/apollo/core/utils/StringUtils.java	82.35% <ø> (+17.53%)	⬆️
...rk/apollo/spring/property/SpringValueRegistry.java	83.78% <0.00%> (-5.41%)	⬇️
.../framework/apollo/spring/property/SpringValue.java	87.71% <0.00%> (-1.76%)	⬇️

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[kezhenxu94]

Seems this method is only used in tests, let's just remove it

[WillardHu]

Removed method and changed the commit message to 'delete unused method StringUtils.join(..)'

[kezhenxu94]

LGTM, although this is kind of breaking changes in apollo-client, I think these 2 methods are not meant to be used by users, and it's easy to migrate to other string util, I'm OK to remove them, WDYT @nobodyiam

[nobodyiam]

@kezhenxu94 I agree with you that it's ok to remove these 2 methods