[SPARK-9723][ML] params getordefault should throw more useful error

[holdenk]

Params.getOrDefault should throw a more meaningful exception than what you get from a bad key lookup.

[srowen]

Can you check if the map contains the param rather than wait for an exception? Really doesn't matter though. This looks OK except that you'll need a space after "param" in the error message below, and you could use string interpolation.

[holdenk]

I figured it was better to handle the exception case this way since the exception case should happen way less frequently. I'll switch it to string interpolation tomorrow :)

[mengxr]

We don't have performance issues here. So code readability is more important, e.g.,

defaultParamMap.getOrElse(param, 
  throw new NoSuchElementException(s"No default value for ${param.name} in ${this.getClass}.")

[SparkQA]

Test build #41918 has finished for PR 8567 at commit 2f6c14d.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #41945 has finished for PR 8567 at commit 1b502b9.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #41949 has finished for PR 8567 at commit 0235a6a.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #41950 has finished for PR 8567 at commit bf324c4.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[mengxr]

LGTM. Merged into master. Thanks!