Remove no-arg constructor and null check for analyticsRouter

analyticsRouter is always provided — only one caller exists
(SQLPlugin.getRestHandlers). Remove the backward-compatible
no-arg constructor and the null check.

Signed-off-by: Kai Huang <ahkcs@amazon.com>

Author: ahkcs

legacy/src/main/java/org/opensearch/sql/legacy/plugin/RestSqlAction.java

@@ -61,7 +61,6 @@
 import org.opensearch.sql.legacy.request.SqlRequestParam;
 import org.opensearch.sql.legacy.rewriter.matchtoterm.VerificationException;
 import org.opensearch.sql.legacy.utils.JsonPrettyFormatter;
-import org.opensearch.sql.legacy.utils.QueryDataAnonymizer;
 import org.opensearch.sql.sql.domain.SQLQueryRequest;
 import org.opensearch.transport.client.Client;
 import org.opensearch.transport.client.node.NodeClient;
@@ -85,16 +84,12 @@ public class RestSqlAction extends BaseRestHandler {
   private final RestSQLQueryAction newSqlQueryHandler;
 
   /**
-   * Optional analytics router. If set, it's called before the normal SQL engine. Accepts the
-   * request and channel, returns {@code true} if it handled the request, {@code false} to fall
-   * through to normal SQL engine.
+   * Analytics router. Called before the normal SQL engine. Accepts the request and channel, returns
+   * {@code true} if it handled the request (analytics index), {@code false} to fall through to
+   * normal SQL engine.
    */
   private final BiFunction<SQLQueryRequest, RestChannel, Boolean> analyticsRouter;
 
-  public RestSqlAction(Settings settings, Injector injector) {
-    this(settings, injector, null);
-  }
-
   public RestSqlAction(
       Settings settings,
       Injector injector,
@@ -160,54 +155,30 @@ protected RestChannelConsumer prepareRequest(RestRequest request, NodeClient cli
 
       // Route to analytics engine for non-Lucene (e.g., Parquet-backed) indices.
       // The router returns true and sends the response directly if it handled the request.
-      if (analyticsRouter != null) {
-        final SQLQueryRequest finalRequest = newSqlRequest;
-        return channel -> {
-          if (!analyticsRouter.apply(finalRequest, channel)) {
-            // Not an analytics query — delegate to normal SQL engine
-            try {
-              newSqlQueryHandler
-                  .prepareRequest(
-                      finalRequest,
-                      (ch, ex) -> {
-                        try {
-                          Format fmt = SqlRequestParam.getFormat(request.params());
-                          QueryAction qa = explainRequest(client, sqlRequest, fmt);
-                          executeSqlRequest(request, qa, client, ch);
-                        } catch (Exception e) {
-                          handleException(ch, e);
-                        }
-                      },
-                      this::handleException)
-                  .accept(channel);
-            } catch (Exception e) {
-              handleException(channel, e);
-            }
+      final SQLQueryRequest finalRequest = newSqlRequest;
+      return channel -> {
+        if (!analyticsRouter.apply(finalRequest, channel)) {
+          // Not an analytics query — delegate to normal SQL engine
+          try {
+            newSqlQueryHandler
+                .prepareRequest(
+                    finalRequest,
+                    (ch, ex) -> {
+                      try {
+                        Format fmt = SqlRequestParam.getFormat(request.params());
+                        QueryAction qa = explainRequest(client, sqlRequest, fmt);
+                        executeSqlRequest(request, qa, client, ch);
+                      } catch (Exception e) {
+                        handleException(ch, e);
+                      }
+                    },
+                    this::handleException)
+                .accept(channel);
+          } catch (Exception e) {
+            handleException(channel, e);
           }
-        };
-      }
-
-      // Route request to new query engine if it's supported already
-      return newSqlQueryHandler.prepareRequest(
-          newSqlRequest,
-          (restChannel, exception) -> {
-            try {
-              if (newSqlRequest.isExplainRequest()) {
-                LOG.info(
-                    "Request is falling back to old SQL engine due to: " + exception.getMessage());
-              }
-              LOG.info(
-                  "[{}] Request {} is not supported and falling back to old SQL engine",
-                  QueryContext.getRequestId(),
-                  newSqlRequest);
-              LOG.info("Request Query: {}", QueryDataAnonymizer.anonymizeData(sqlRequest.getSql()));
-              QueryAction queryAction = explainRequest(client, sqlRequest, format);
-              executeSqlRequest(request, queryAction, client, restChannel);
-            } catch (Exception e) {
-              handleException(restChannel, e);
-            }
-          },
-          this::handleException);
+        }
+      };
     } catch (Exception e) {
       return channel -> handleException(channel, e);
     }