FileLayerDeleter will throw NullPointerException

[lossyrob]

Setup:

Have a File catalog in a state where a layer "exists", in that it has metadata in the attribute store, but the directory path pointed to by the FileLayerHeader.path for that layer does not exist.

Expected:

The FileLayerDeleter delete method will see that there's no file there, and move along exceptionless.

Actual:

It blows up with a null pointer exception with the following stack trace:

error] (run-main-0) java.lang.NullPointerException
java.lang.NullPointerException
        at scala.collection.mutable.ArrayOps$ofRef$.length$extension(ArrayOps.scala:192)
        at scala.collection.mutable.ArrayOps$ofRef.length(ArrayOps.scala:192)
        at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:32)
        at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186)
        at geotrellis.spark.io.file.FileLayerDeleter$$anon$1.delete(FileLayerDeleter.scala:36)
        at geotrellis.spark.io.file.FileLayerDeleter$$anon$1.delete(FileLayerDeleter.scala:16)
        at geotrellis.spark.io.file.FileLayerManager.delete(FileLayerManager.scala:20)

Problem code exists here:

geotrellis/spark/src/main/scala/geotrellis/spark/io/file/FileLayerDeleter.scala

Lines 49 to 55 in e0b98d9

	val sourceLayerPath = new File(attributeStore.catalogPath, header.path)
	sourceLayerPath
	.listFiles()
	.foreach(_.delete())
	sourceLayerPath.delete
	}

The issue should be fixed by checking sourceLayerPath exists before doing anything with it.

Thanks to @cepkoCC for the bug report.

[cepkoCC]

On it!