Bugfix fix

Author: janniklinde

src/main/java/org/apache/sysds/hops/rewriter/RewriterRuleCollection.java

@@ -1675,9 +1675,7 @@ public static void canonicalExpandAfterFlattening(final List<RewriterRule> rules
 								.as(UUID.randomUUID().toString())
 								.withInstruction("sum")
 								.withOps(newIdxExpr);
-						System.out.println("Copying index list: " + newIdxExpr.toParsableString(ctx));
 						RewriterUtils.copyIndexList(newIdxExpr);
-						System.out.println("After copy: " + newIdxExpr.toParsableString(ctx));
 						newIdxExpr.refreshReturnType(ctx);
 						newSum.consolidate(ctx);
 						newArgList.getOperands().add(newSum);

src/main/java/org/apache/sysds/hops/rewriter/utils/RewriterUtils.java

@@ -869,7 +869,8 @@ public static void copyIndexList(RewriterStatement idxExprRoot) {
 			return null;
 		});
 
-		idxExprRoot.getOperands().set(1, out);
+		if (out != null)
+			idxExprRoot.getOperands().set(1, out);
 	}
 
 	public static void retargetIndexExpressions(RewriterStatement rootExpr, UUID oldIdxId, RewriterStatement newStatement) {