fix: tokenAssociate throws IndexOutOfBoundsException (#12453) (#12550)

Signed-off-by: Zhivko Kelchev <[email protected]>
Co-authored-by: Valentin Tronkov <[email protected]>

Author: JivkoKelchev

hedera-node/hedera-token-service-impl/src/main/java/com/hedera/node/app/service/token/impl/handlers/BaseTokenHandler.java

@@ -170,22 +170,26 @@ protected void createAndLinkTokenRels(
             @NonNull final WritableTokenRelationStore tokenRelStore) {
         // create list of token relations to be added
         final var newTokenRels = createTokenRelsToAccount(account, tokens);
-        // Link the new token relations to the account
-        linkTokenRels(account, newTokenRels, tokenRelStore);
-
-        // Now replace the account's old head token number with the new head token number. This is
-        // how we link the new tokenRels to the account
-        final var firstOfNewTokenRels = newTokenRels.get(0);
-        final var updatedAcct = account.copyBuilder()
-                // replace the head token number with the first token number of the new tokenRels
-                .headTokenId(firstOfNewTokenRels.tokenId())
-                // and also update the account's total number of token associations
-                .numberAssociations(account.numberAssociations() + newTokenRels.size())
-                .build();
 
-        // Save the results
-        accountStore.put(updatedAcct);
-        newTokenRels.forEach(tokenRelStore::put);
+        // FUTURE - We may need to return a proper error status when tokens are empty
+        if (!newTokenRels.isEmpty()) {
+            // Link the new token relations to the account
+            linkTokenRels(account, newTokenRels, tokenRelStore);
+
+            // Now replace the account's old head token number with the new head token number. This is
+            // how we link the new tokenRels to the account
+            final var firstOfNewTokenRels = newTokenRels.get(0);
+            final var updatedAcct = account.copyBuilder()
+                    // replace the head token number with the first token number of the new tokenRels
+                    .headTokenId(firstOfNewTokenRels.tokenId())
+                    // and also update the account's total number of token associations
+                    .numberAssociations(account.numberAssociations() + newTokenRels.size())
+                    .build();
+
+            // Save the results
+            accountStore.put(updatedAcct);
+            newTokenRels.forEach(tokenRelStore::put);
+        }
     }
 
     /**