code: def validate_kernel_string(self, kernel):
          
          if kernel:
              if '/' not in kernel:
                  raise ValueError('Kernel must be specified in the form of '
                                   '\'{username}/{kernel-slug}\'')
  
              split = kernel.split('/')
              if not split[0] or not split[1]:
                  raise ValueError('Kernel must be specified in the form of '
                                   '\'{username}/{kernel-slug}\'')
  
              if len(split[1]) < 5:
                  raise ValueError(
                      'Kernel slug must be at least five characters')
docs: determine if a kernel string is valid, meaning it is in the format
              of {username}/{kernel-slug}.
               Parameters
              ==========
              kernel: the kernel name to validate