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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def merge(directory=None, revisions='', message=None, branch_label=None, rev_id=None):
 """Merge two revisions together. Creates a new migration file"""

    if alembic_version >= (0, 7, 0):
        config = current_app.extensions['migrate'].migrate.get_config(
            directory)
        command.merge(config, revisions, message=message,
                      branch_label=branch_label, rev_id=rev_id)
    else:
        raise RuntimeError('Alembic 0.7.0 or greater is required')