Updating contribution to Completed for manually entered Membership fails

I created a Membership in the admin, indicating a pay later contribution. When updating the contribution status, there is an error in line 1073 of CRM/Contribute/Form/Contribution.php, where this line fails :

$this->_priceSetId = CRM_Core_DAO::getFieldValue('CRM_Price_DAO_Field', $lineItems[$itemId]['price_field_id'], 'price_set_id');

because the second parameter to getFieldValue is NULL. The getFieldValue code ungracefully dies on that.

I have fixed it by wrapping the code section in an if (!empty($lineItems)) block, which works, but I am unsure whether this is the correct approach.