Tidy JavaDoc and fix error in getTop5ErrorMetrics method.

[ham1]

Description

Fixed bug whereby calling registerError with the following data set ["A", "B", "C", "D", "E", "F"] would return [["A", 1], [null, null], [null, null], [null, null], [null, null]] instead of [["A", 1], ["B", 1], ["C", 1], ["D", 1], ["E", 1]].

Improved JavaDoc for registerError
Also removed JavaDoc which did not add anything to the method names.

Motivation and Context

Made the code more readable and at the same time fixed a subtle error.

How Has This Been Tested?

On my spock branch:

    def "errors with the same frequency are preserved up until the size limit"() {
        given:
            def testData = ["A", "B", "C", "D", "E", "F"]
            for (def key : testData) {
                sut.registerError(key)
            }
        expect:
            sut.getTop5ErrorsMetrics() == [["A", 1], ["B", 1], ["C", 1], ["D", 1], ["E", 1]]
    }

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.

[codecov-io]

Codecov Report

Merging #337 into trunk will increase coverage by <.01%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##             trunk     #337      +/-   ##
===========================================
+ Coverage     57.9%   57.91%   +<.01%     
- Complexity   10023    10025       +2     
===========================================
  Files         1148     1148              
  Lines        73798    73792       -6     
  Branches      7331     7329       -2     
===========================================
+ Hits         42732    42735       +3     
+ Misses       28587    28578       -9     
  Partials      2479     2479

Impacted Files	Coverage Δ	Complexity Δ
...jmeter/report/processor/Top5ErrorsSummaryData.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...apache/jmeter/extractor/TestBoundaryExtractor.java	97.88% <0%> (ø)	17% <0%> (ø)	⬇️
...c/core/org/apache/jmeter/reporters/Summariser.java	86.15% <0%> (+0.76%)	19% <0%> (+1%)	⬆️
...s/org/apache/jmeter/timers/PoissonRandomTimer.java	78.37% <0%> (+5.4%)	10% <0%> (+1%)	⬆️

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