[TEST] Ensure reflectively created Lists always have at least one element

Fixes an issue in the test where the class can be constructed but fails to
replace its children due to validation of the number of elements in the list.

Original commit: elastic/x-pack-elasticsearch@3199318d9c

plugin/sql/src/test/java/org/elasticsearch/xpack/sql/tree/NodeSubclassTests.java

@@ -346,7 +346,7 @@ public class NodeSubclassTests<T extends B, B extends Node<B>> extends ESTestCas
                 return map;
             }
             if (pt.getRawType() == List.class) {
-                return makeList(toBuildClass, pt, between(0, 10));
+                return makeList(toBuildClass, pt, between(1, 10));
             }
             if (pt.getRawType() == Supplier.class) {
                 if (toBuildClass == AggValueInput.class) {