Empty barcode

**[Original report](https://bitbucket.org/laborstudents/chemical-inventory-new/issue/160) by Benjamin Quesada (Bitbucket: [benrquesada](https://bitbucket.org/benrquesada), GitHub: [benrquesada](https://github.com/benrquesada)).**

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A container can be created without a barcode when you select "Manually enter a barcode" and put nothing in the box and click submit you then create a chemical with no barcode. this can only happen once in the database but it is still an issue since the chemical can not be deleted nor checked.

Reproduce the flow described: create a container, choose "Manually enter a barcode," leave the field empty, and submit. Trace the validation and chemical-creation entry points to determine where empty barcodes are accepted; done means the submission is rejected and no chemical without a barcode can be created.

Written by the indexing model from the issue text.