opt(common): GenesisBlock timestamp valid message error

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

Author: imalasong

common/src/main/java/org/tron/common/args/GenesisBlock.java

@@ -61,18 +61,17 @@ public void setAssets(final List<Account> assets) {
    */
   public void setTimestamp(final String timestamp) {
     this.timestamp = timestamp;
-
     if (this.timestamp == null) {
       this.timestamp = DEFAULT_TIMESTAMP;
-    }
-
-    try {
-      long l = Long.parseLong(this.timestamp);
-      if (l < 0) {
+    } else {
+      try {
+        long l = Long.parseLong(this.timestamp);
+        if (l < 0) {
+          throw new IllegalArgumentException("Timestamp(" + timestamp + ") must be greater than or equal to 0.");
+        }
+      } catch (NumberFormatException e) {
         throw new IllegalArgumentException("Timestamp(" + timestamp + ") must be a Long type.");
       }
-    } catch (NumberFormatException e) {
-      throw new IllegalArgumentException("Timestamp(" + timestamp + ") must be a Long type.");
     }
   }