Thank you @apmuthu
I resolved it by creating a sales person which i set as the default for the company. On creating new customer, its auto assigned the sales person thus resolving the NULL issue in the field in the table "0_salesman"

It's a new installation with version 2.4.8 running on a web server.
I'm able to create new suppliers just fine, ironically i can't  create new customers. I have this setting under setup:
Company Setup>>Search Customer List, and Search Supplier List both UNCHECKED.

for troubleshooting I turned on debugging in config.php ($go_debug =1;)
this is the error output when i attempt to create a new customer;

DATABASE ERROR : The branch record could not be added
error code : 1366
error message : Incorrect integer value: '' for column `delcom_fdb-31343xxxx`.`0_cust_branch`.`salesman` at row 1
sql that failed was : INSERT INTO 0_cust_branch (debtor_no, br_name, branch_ref, br_address, salesman, area, tax_group_id, sales_account, receivables_account, payment_discount_account, sales_discount_account, default_location, br_post_address, group_no, default_ship_via, notes, bank_account) VALUES ('29','TEST customer', 'TS c', '', '', '1','1', '', '1200', '4500', '4510', 'DEF', '','0', '1', '', NULL)

I don't what i missed, would appreciate some fast help, thanks