<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_workflow_definitions(sbi_config: dict):
 """Add any missing SBI workflow definitions as placeholders. This is a utility function used in testing and adds mock / test workflow definitions to the database for workflows defined in the specified SBI config. Args: sbi_config (dict):
 SBI configuration dictionary. """

    registered_workflows = []
    for i in range(len(sbi_config['processing_blocks'])):
        workflow_config = sbi_config['processing_blocks'][i]['workflow']
        workflow_name = '{}:{}'.format(workflow_config['id'],
                                       workflow_config['version'])
        if workflow_name in registered_workflows:
            continue
        workflow_definition = dict(
            id=workflow_config['id'],
            version=workflow_config['version'],
            stages=[]
        )
        key = "workflow_definitions:{}:{}".format(workflow_config['id'],
                                                  workflow_config['version'])
        DB.save_dict(key, workflow_definition, hierarchical=False)
        registered_workflows.append(workflow_name)