AML UI: UI doesnt save a new merchant when we use a new merchantID (rare scenario)

The Merchant ID that is used and edited say Merchant ID is x1 and edited to x2, and when we try to create a new merchant with x1 then its not saving merchant details and throwing exception in the tomcat log.

Steps to reproduce

1. Login to reseller UI with valid credentials.
2. Click Merchants tab.
3. Click Create Merchant Button.
4. Enter the Merchant Name say Merchant_Name, Merchant ID say Merchant_ID and other details.
5. Click Save button.
6. For the created merchant edit the merchant id from Merchant_ID to Merchant_ID_New.
7. Click Save button and the merchant is saved successfully.
8. Click Create Merchant Button.
9. Enter the merchant Name Say Merchant_Name2, and same Merchant ID that was used in step4. Which is Merchant_ID.
10. Click Save button.

Expected:
Merchant should get saved when save button is clicked.

Actual:
Merchant is not saved when we click save button and no error message.

Please find the attached tomcat log.

Log Location : Tomcat server (198.61.203.70) tail -f /tmp/log/tomcat6/aml.log