I Can't able to delete a company after being created giving error as

The operation cannot be completed, probably due to the following:

- deletion: you may be trying to delete a record while other records still reference it

- creation/update: a mandatory field is not correctly set

[object with reference: Company - res.company]

But when trying to delete from SQL Line It shows as

ERROR: null value in column "partner_id" violates not-null constraint

DETAIL: Failing row contains (12, ACCOUNTS, null, 21, null, 2017-03-10 07:35:53.81076,

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<frame id="first" x1="1.3cm..., a4, 1, iVBORw0KGgoAAAANSUhEUgAAALQAAAAqCAYAAAAaoXEBAAAiZElEQVR4nO2de4yc..., 1, null, null, account@prakruti.com, 1, f, null,

<header>.........more info

Please can anyone help me on this