diff --git a/src/main/java/org/broadinstitute/hellbender/tools/dragstr/CalibrateDragstrModel.java b/src/main/java/org/broadinstitute/hellbender/tools/dragstr/CalibrateDragstrModel.java
index d3e68a39218..24bb5df696f 100644
--- a/src/main/java/org/broadinstitute/hellbender/tools/dragstr/CalibrateDragstrModel.java
+++ b/src/main/java/org/broadinstitute/hellbender/tools/dragstr/CalibrateDragstrModel.java
@@ -1,9 +1,32 @@
 package org.broadinstitute.hellbender.tools.dragstr;
 
-import htsjdk.samtools.*;
-import htsjdk.samtools.cram.ref.ReferenceSource;
-import htsjdk.samtools.util.IntervalTree;
-import it.unimi.dsi.fastutil.ints.*;
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.EnumSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.Spliterator;
+import java.util.Vector;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.BiConsumer;
+import java.util.function.BinaryOperator;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Collector;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
 import org.apache.commons.io.output.NullOutputStream;
 import org.broadinstitute.barclay.argparser.Argument;
 import org.broadinstitute.barclay.argparser.ArgumentCollection;
@@ -11,12 +34,20 @@
 import org.broadinstitute.barclay.help.DocumentedFeature;
 import org.broadinstitute.hellbender.cmdline.StandardArgumentDefinitions;
 import org.broadinstitute.hellbender.cmdline.programgroups.ShortVariantDiscoveryProgramGroup;
-import org.broadinstitute.hellbender.engine.*;
+import org.broadinstitute.hellbender.engine.GATKPath;
+import org.broadinstitute.hellbender.engine.GATKTool;
+import org.broadinstitute.hellbender.engine.ReadsDataSource;
+import org.broadinstitute.hellbender.engine.ReadsPathDataSource;
 import org.broadinstitute.hellbender.exceptions.GATKException;
 import org.broadinstitute.hellbender.tools.walkers.haplotypecaller.HaplotypeCaller;
 import org.broadinstitute.hellbender.transformers.DRAGENMappingQualityReadTransformer;
 import org.broadinstitute.hellbender.transformers.ReadTransformer;
-import org.broadinstitute.hellbender.utils.*;
+import org.broadinstitute.hellbender.utils.BinaryTableReader;
+import org.broadinstitute.hellbender.utils.IntervalMergingRule;
+import org.broadinstitute.hellbender.utils.IntervalUtils;
+import org.broadinstitute.hellbender.utils.SequenceDictionaryUtils;
+import org.broadinstitute.hellbender.utils.SimpleInterval;
+import org.broadinstitute.hellbender.utils.Utils;
 import org.broadinstitute.hellbender.utils.collections.AutoCloseableCollection;
 import org.broadinstitute.hellbender.utils.dragstr.DragstrParamUtils;
 import org.broadinstitute.hellbender.utils.dragstr.DragstrParams;
@@ -24,14 +55,21 @@
 import org.broadinstitute.hellbender.utils.gcs.BucketUtils;
 import org.broadinstitute.hellbender.utils.read.GATKRead;
 import org.broadinstitute.hellbender.utils.reference.AbsoluteCoordinates;
-import scala.Tuple4;
 
-import java.io.IOException;
-import java.io.PrintWriter;
-import java.util.*;
-import java.util.concurrent.atomic.AtomicLong;
-import java.util.function.*;
-import java.util.stream.*;
+import htsjdk.samtools.CigarElement;
+import htsjdk.samtools.CigarOperator;
+import htsjdk.samtools.SAMFlag;
+import htsjdk.samtools.SAMReadGroupRecord;
+import htsjdk.samtools.SAMRecord;
+import htsjdk.samtools.SAMSequenceDictionary;
+import htsjdk.samtools.SamReaderFactory;
+import htsjdk.samtools.util.IntervalTree;
+import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
+import it.unimi.dsi.fastutil.ints.Int2ObjectMaps;
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
+import it.unimi.dsi.fastutil.ints.IntArrayList;
+import it.unimi.dsi.fastutil.ints.IntList;
+import scala.Tuple4;
 
 /**
  * Estimates the parameters for the DRAGstr model for an input sample.
@@ -500,7 +538,7 @@ private StratifiedDragstrLocusCases collectCaseStatsParallel(final List<SimpleIn
 
         final List<SimpleInterval> shards = shardIntervals(intervals, shardSize);
 
-        final List<ReadsPathDataSource> readSources = new ArrayList<>(threads);
+        final Collection<ReadsPathDataSource> readSources = new Vector<>(threads);
         final ThreadLocal<ReadsPathDataSource> threadReadSource = ThreadLocal.withInitial(
                 () -> {
                     final ReadsPathDataSource result = new ReadsPathDataSource(readArguments.getReadPaths(), factory);
@@ -1033,4 +1071,4 @@ public String toString() {
             return "(" +  period + ',' + repeatLength + ')';
         }
     }
-}
\ No newline at end of file
+}