Product collection join with product custom attribute with custom table – undefined column

I am working with some product collection join with custom table, I’ve a custom product attribute, need to add a join condition with the product custom attribute with the custom table attribute.

The custom table is agreements and in product we’re also has a custom attribute called agreement, when i tried to join as like below i am getting error like agreement is undefined field (agreement is a product custom attribute – select)

    $this->_collection->getSelect()->joinLeft(
                ['agreement_table'=>'agreements'],
                'e.agreement = agreement_table.id',
                []
   );

Thanks in advance for your better support.