fixListBug (#541)

* fixListBug

Signed-off-by: xinyual <[email protected]>

* fixListBug

Signed-off-by: xinyual <[email protected]>

---------

Signed-off-by: xinyual <[email protected]>

Author: xinyual

src/main/java/org/opensearch/agent/tools/PPLTool.java

@@ -559,8 +559,15 @@ private static void extractSamples(Map<String, Object> sampleSource, Map<String,
         for (Map.Entry<String, Object> entry : sampleSource.entrySet()) {
             String p = entry.getKey();
             Object v = entry.getValue();
-            while (v instanceof List<?>) {
-                v = ((List<?>) v).get(0);
+
+            while (!Objects.isNull(v) && v instanceof List<?>) {
+                List<?> listValue = (List<?>) v;
+                if (!listValue.isEmpty()) {
+                    v = ((List<?>) v).get(0);
+                } else {
+                    break;
+                }
+
             }
 
             String fullKey = prefix + p;