code: func anyClientNilResultValueSpec(spec *MethodSpec, method string) *MethodSpec {
  	// Commands that can return nil/zero-value given random input and state
  	switch method {
  	// Redis-Spec: DB may be empty and AllKeys can return nil result
  	// REVU: check if this is actually conformant
  	case "AllKeys":
  		spec.NoNilResultValue = false
  	}
  
  	return spec
  }
docs: // spec.NoNilResultValue
  // Specs MethodSpec.NoNilResultValue - client type invariant