PSOParamGeneratorTest test failure

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Seeing the following test failure when running `play_command $OPTS clean test compile dist`:

```
[info] Total for test com.linkedin.drelephant.mapreduce.fetchers.MapReduceFSFetcherHadoop2Test
[info] Finished in 0.0 seconds
[info] 5 tests, 0 failures, 0 errors
[error] Test com.linkedin.drelephant.tuning.PSOParamGeneratorTest.getParamsTest failed: Swarm size did not match expected:<3> but was:<0>
[error] Test com.linkedin.drelephant.tuning.PSOParamGeneratorTest.generateParamSetTest failed: java.lang.RuntimeException: java.lang.NullPointerException
[error] at play.libs.Json.parse(Json.java:71)
[error] at com.linkedin.drelephant.tuning.PSOParamGeneratorTest$2.run(PSOParamGeneratorTest.java:111)
[error] at play.test.Helpers.running(Helpers.java:417)
[error] at com.linkedin.drelephant.tuning.PSOParamGeneratorTest.generateParamSetTest(PSOParamGeneratorTest.java:79)
[error] ...
[error] Caused by: java.lang.NullPointerException
[error] at com.fasterxml.jackson.core.JsonFactory.createParser(JsonFactory.java:822)
[error] at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2580)
[error] at play.libs.Json.parse(Json.java:69)
[error] ... 40 more
```

Reproduce the report with `play_command $OPTS clean test compile dist`, then inspect `PSOParamGeneratorTest.getParamsTest` and `generateParamSetTest`, especially the referenced lines 79 and 111. Done means both tests pass without the swarm-size mismatch or the JSON parsing NullPointerException.

Written by the indexing model from the issue text.