fix(config): trustNode default empty when not configured

Previously config.hasPath returned false when trustNode was commented
out, resulting in trustNodeAddr=null. Bean binding always provided
a default value '127.0.0.1:50051', changing behavior. Restore null
semantics by defaulting to empty string and converting to null.

Author: vividctrlalt

common/src/main/java/org/tron/core/config/args/NodeConfig.java

@@ -35,7 +35,7 @@
 public class NodeConfig {
 
   // ---- Flat scalar fields (auto-bound by ConfigBeanFactory) ----
-  private String trustNode = "127.0.0.1:50051";
+  private String trustNode = "";
   private boolean walletExtensionApi = true;
   private int syncFetchBatchNum = 2000;
   private int validateSignThreadNum = Runtime.getRuntime().availableProcessors();
@@ -321,7 +321,7 @@ public static class DnsConfig {
     int cpus = Runtime.getRuntime().availableProcessors();
     StringBuilder sb = new StringBuilder();
     // flat scalars
-    sb.append("trustNode = \"127.0.0.1:50051\"\n");
+    sb.append("trustNode = \"\"\n");
     sb.append("walletExtensionApi = true\n");
     sb.append("syncFetchBatchNum = 2000\n");
     sb.append("validateSignThreadNum = ").append(cpus).append("\n");

framework/src/main/java/org/tron/core/config/args/Args.java

@@ -656,7 +656,8 @@ private static void applyNodeConfig(NodeConfig nc) {
     PARAMETER.udpNettyWorkThreadNum = nc.getUdpNettyWorkThreadNum();
 
     if (StringUtils.isEmpty(PARAMETER.trustNodeAddr)) {
-      PARAMETER.trustNodeAddr = nc.getTrustNode();
+      String trustNode = nc.getTrustNode();
+      PARAMETER.trustNodeAddr = StringUtils.isEmpty(trustNode) ? null : trustNode;
     }
 
     PARAMETER.validateSignThreadNum = nc.getValidateSignThreadNum();