Converting null collection Java<->Scala yields null

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When a null value is cast as a Java collection, and an implicit converter from scala.collection.convert.WrapAsScala is in scope, the converter will be passed null and return a wrapped collection with null as the underlying collection. Calling any bridge method provided by the wrapper will result in a NullPointerException. This can cause unexpected behavior in an application that relies on interacting with a wrapper collection, but does not have access to the underlying java reference in order to determine whether it is a collection or null. In this scenario, the application gets the collection wrapper via whatever means, and tries to operate upon it - thus generating a somewhat counter-intuitive exception.

An example of this issue in the wild can be seen at scalafx issue #178, and an example of code that generates such a wrapper before the issue was fixed.

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Imported From: https://issues.scala-lang.org/browse/SI-9113?orig=1
Reporter: @RomanHargrave
Affected Versions: 2.11.2, 2.11.4

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@RomanHargrave said:
Added a test suite to demonstrate null conversion bug.

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@RomanHargrave said:
I have opened pr #4266, which fixes this issue.

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@RomanHargrave said:
The previous PR had some problems with jenkins, so I have closed it and opened #4267 in its place.

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@adriaanm said:
Slight reword in scala/scala#4327

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@adriaanm said:
scala/scala#4343