PARQUET-2498. Vector IO to handle empty range list

Empty range lists currently trigger IllegalArgumentException,
however some (integration test) codepaths attempt to do this.

Downgrading the empty list case to a no-op resolves this.

Contributed by Steve Loughran

Change-Id: I07ed7e8f0628e170441a2d0679e822d23cfb1440

parquet-hadoop/src/main/java/org/apache/parquet/hadoop/util/wrapped/io/VectorIoBridge.java

@@ -362,7 +362,12 @@ private static ParquetFileRange validateRangeRequest(ParquetFileRange range) {
   private static List<ParquetFileRange> validateAndSortRanges(final List<ParquetFileRange> input) {
 
     requireNonNull(input, "Null input list");
-    checkArgument(!input.isEmpty(), "Empty input list");
+    if (input.isEmpty()) {
+      // this may seem a pathological case, but it
+      // has surfaced during testing.
+      LOG.debug("Empty input list");
+      return input;
+    }
     final List<ParquetFileRange> sortedRanges;
 
     if (input.size() == 1) {

parquet-hadoop/src/test/java/org/apache/parquet/hadoop/util/wrapped/io/TestVectorIoBridge.java

@@ -305,6 +305,17 @@ public void testNullRangeList() throws Exception {
     verifyExceptionalVectoredRead(null, NullPointerException.class);
   }
 
+  /**
+   * An empty range list is permitted.
+   */
+  @Test
+  public void testEmptyRangeList() throws Exception {
+    List<ParquetFileRange> fileRanges = new ArrayList<>();
+    try (FSDataInputStream in = openTestFile()) {
+      readVectored(in, fileRanges);
+    }
+  }
+
   @Test
   public void testSomeRandomNonOverlappingRanges() throws Exception {
     List<ParquetFileRange> fileRanges = ranges(