{"record":{"id":"19f4d37cc5ddc16e","repo":"hyperledger/fabric","slug":"first-block-is-nil","errorCode":null,"errorMessage":"first block is nil","messagePattern":"first block is nil","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"orderer/common/follower/block_puller.go","lineNumber":154,"sourceCode":"\tif err != nil {\n\t\treturn errors.WithMessage(err, \"failed to extract config envelope from block\")\n\t}\n\tverifier, err := creator.blockSigVerifierFactory.VerifierFromConfig(configEnv, creator.channelID)\n\tif err != nil {\n\t\treturn errors.WithMessage(err, \"failed to construct a block signature verifier from config envelope\")\n\t}\n\tcreator.blockSigVerifier = verifier\n\treturn nil\n}\n\n// VerifyBlockSequence verifies a sequence of blocks, using the internal block signature verifier. It also bootstraps\n// the block sig verifier form the genesis block if it does not exist, and skips verifying the genesis block.\nfunc (creator *BlockPullerCreator) VerifyBlockSequence(blocks []*common.Block, _ string) error {\n\tif len(blocks) == 0 {\n\t\treturn errors.New(\"buffer is empty\")\n\t}\n\tif blocks[0] == nil {\n\t\treturn errors.New(\"first block is nil\")\n\t}\n\tif blocks[0].Header == nil {\n\t\treturn errors.New(\"first block header is nil\")\n\t}\n\tif blocks[0].Header.Number == 0 {\n\t\tif creator.JoinBlock != nil && creator.JoinBlock.Header.Number == 0 {\n\t\t\t// If we have joined with a genesis block,\n\t\t\t// replace the genesis block we got from the network\n\t\t\t// with our own.\n\t\t\tblocks[0] = creator.JoinBlock\n\t\t}\n\t\tconfigEnv, err := deliverclient.ConfigFromBlock(blocks[0])\n\t\tif err != nil {\n\t\t\treturn errors.WithMessage(err, \"failed to extract config envelope from genesis block\")\n\t\t}\n\t\t// Bootstrap the verifier from the genesis block, as it will be used to verify\n\t\t// the subsequent blocks in the batch.\n\t\tcreator.blockSigVerifier, err = creator.blockSigVerifierFactory.VerifierFromConfig(configEnv, creator.channelID)","sourceCodeStart":136,"sourceCodeEnd":172,"githubUrl":"https://github.com/hyperledger/fabric/blob/2736b63f8fd5932511d56fe68b7039d15977f7f6/orderer/common/follower/block_puller.go#L136-L172","documentation":"VerifyBlockSequence requires the first block of the sequence to be non-nil because it bootstraps signature verification from blocks[0]. A nil element means the producer of the slice emitted a placeholder, which cannot be verified.","triggerScenarios":"Calling VerifyBlockSequence with a slice whose first element is nil — usually a puller or buffer that appends a nil on error instead of skipping, or manual construction of the slice in tests/tools.","commonSituations":"Custom block-buffer implementations between puller and verifier appending nil entries; gRPC decode failure leaving a nil slot; test harnesses pre-allocating make([]*common.Block, n) without filling elements.","solutions":["Fix the producer (puller/buffer) to never append nil blocks; drop failed blocks and adjust the sequence","Filter nil entries out of the slice before calling VerifyBlockSequence","If pre-allocating, fill the slice with real blocks before verification"],"exampleFix":"// before\nblocks := make([]*common.Block, len(pulled))\ncreator.VerifyBlockSequence(blocks, channelID)\n// after\nvar blocks []*common.Block\nfor _, b := range pulled {\n    if b != nil {\n        blocks = append(blocks, b)\n    }\n}\ncreator.VerifyBlockSequence(blocks, channelID)","handlingStrategy":"type-guard","validationCode":"func isVerifiableSequence(blocks []*common.Block) bool {\n    return len(blocks) > 0 && blocks[0] != nil\n}\n// guard before calling VerifyBlockSequence","typeGuard":"func firstBlockPresent(blocks []*common.Block) bool {\n    return len(blocks) > 0 && blocks[0] != nil && blocks[0].Header != nil\n}","tryCatchPattern":"if err := creator.VerifyBlockSequence(blocks, channelID); err != nil {\n    if err.Error() == \"first block is nil\" {\n        return fmt.Errorf(\"pull buffer produced nil block; inspect puller/buffer implementation\")\n    }\n    return err\n}","preventionTips":["Never append nil blocks to pull buffers; skip and re-pull instead","Avoid make([]*common.Block, n) preallocation that can leave nil slots","Surface unmarshal errors instead of inserting empty entries"],"tags":["blocks","nil-pointer","verification"],"backgroundTag":"nil-block-in-sequence","analyzedSha":"2736b63f8fd5932511d56fe68b7039d15977f7f6","analyzedAt":"2026-09-04T08:52:36.465Z","contentChangedAt":"2026-09-04T08:52:36.465Z","schemaVersion":2},"datasetVersion":"2026-09-08T10:18:20.063Z"}