diff --git a/Gododir/main.go b/Gododir/main.go
index 44456216..745bb16d 100644
--- a/Gododir/main.go
+++ b/Gododir/main.go
@@ -64,7 +64,7 @@ func tasks(p *do.Project) {
 				"environment":  environment,
 				"contractHash": contractHash,
 				"abiFilepath":  abiFilepath,
-				"$in":          "cmd/subscribe_contract",
+				"$in":          "cmd/watch_contract",
 			})
 	})
 
diff --git a/cmd/subscribe_contract/main.go b/cmd/watch_contract/main.go
similarity index 100%
rename from cmd/subscribe_contract/main.go
rename to cmd/watch_contract/main.go
diff --git a/pkg/contract_summary/summary.go b/pkg/contract_summary/summary.go
index fea42f9f..98e26ee5 100644
--- a/pkg/contract_summary/summary.go
+++ b/pkg/contract_summary/summary.go
@@ -1,9 +1,6 @@
 package contract_summary
 
 import (
-	"errors"
-	"fmt"
-
 	"math/big"
 
 	"github.com/8thlight/vulcanizedb/pkg/core"
@@ -20,16 +17,12 @@ type ContractSummary struct {
 	blockChain           core.Blockchain
 }
 
-var ErrContractDoesNotExist = func(contractHash string) error {
-	return errors.New(fmt.Sprintf("Contract %v does not exist", contractHash))
-}
-
 func NewSummary(blockchain core.Blockchain, repository repositories.Repository, contractHash string, blockNumber *big.Int) (ContractSummary, error) {
-	contract := repository.FindContract(contractHash)
-	if contract != nil {
-		return newContractSummary(blockchain, *contract, blockNumber), nil
+	contract, err := repository.FindContract(contractHash)
+	if err != nil {
+		return ContractSummary{}, err
 	} else {
-		return ContractSummary{}, ErrContractDoesNotExist(contractHash)
+		return newContractSummary(blockchain, contract, blockNumber), nil
 	}
 }
 
diff --git a/pkg/history/populate_blocks_test.go b/pkg/history/populate_blocks_test.go
index 1b3c772b..0dcc7aee 100644
--- a/pkg/history/populate_blocks_test.go
+++ b/pkg/history/populate_blocks_test.go
@@ -19,8 +19,8 @@ var _ = Describe("Populating blocks", func() {
 
 		history.PopulateBlocks(blockchain, repository, 1)
 
-		block := repository.FindBlockByNumber(1)
-		Expect(block).NotTo(BeNil())
+		block, err := repository.FindBlockByNumber(1)
+		Expect(err).ToNot(HaveOccurred())
 		Expect(block.Hash).To(Equal("x012343"))
 	})
 
@@ -45,11 +45,16 @@ var _ = Describe("Populating blocks", func() {
 		history.PopulateBlocks(blockchain, repository, 5)
 
 		Expect(repository.BlockCount()).To(Equal(11))
-		Expect(repository.FindBlockByNumber(4)).To(BeNil())
-		Expect(repository.FindBlockByNumber(5)).NotTo(BeNil())
-		Expect(repository.FindBlockByNumber(8)).NotTo(BeNil())
-		Expect(repository.FindBlockByNumber(10)).NotTo(BeNil())
-		Expect(repository.FindBlockByNumber(13)).To(BeNil())
+		_, err := repository.FindBlockByNumber(4)
+		Expect(err).To(HaveOccurred())
+		_, err = repository.FindBlockByNumber(5)
+		Expect(err).ToNot(HaveOccurred())
+		_, err = repository.FindBlockByNumber(8)
+		Expect(err).ToNot(HaveOccurred())
+		_, err = repository.FindBlockByNumber(10)
+		Expect(err).ToNot(HaveOccurred())
+		_, err = repository.FindBlockByNumber(13)
+		Expect(err).To(HaveOccurred())
 	})
 
 	It("returns the number of blocks created", func() {
diff --git a/pkg/observers/blockchain_db_observer_test.go b/pkg/observers/blockchain_db_observer_test.go
index 0f510095..38a254ae 100644
--- a/pkg/observers/blockchain_db_observer_test.go
+++ b/pkg/observers/blockchain_db_observer_test.go
@@ -30,8 +30,8 @@ var _ = Describe("Saving blocks to the database", func() {
 		observer := observers.NewBlockchainDbObserver(repository)
 		observer.NotifyBlockAdded(block)
 
-		savedBlock := repository.FindBlockByNumber(123)
-		Expect(savedBlock).NotTo(BeNil())
+		savedBlock, err := repository.FindBlockByNumber(123)
+		Expect(err).ToNot(HaveOccurred())
 		Expect(len(savedBlock.Transactions)).To(Equal(1))
 	})
 
diff --git a/pkg/repositories/in_memory.go b/pkg/repositories/in_memory.go
index 9e0bac9c..b2a0de6c 100644
--- a/pkg/repositories/in_memory.go
+++ b/pkg/repositories/in_memory.go
@@ -7,8 +7,8 @@ import (
 )
 
 type InMemory struct {
-	blocks    map[int64]*core.Block
-	contracts map[string]*core.Contract
+	blocks    map[int64]core.Block
+	contracts map[string]core.Contract
 	logs      map[string][]core.Log
 }
 
@@ -34,7 +34,7 @@ func (repository *InMemory) FindLogs(address string, blockNumber int64) []core.L
 }
 
 func (repository *InMemory) CreateContract(contract core.Contract) error {
-	repository.contracts[contract.Hash] = &contract
+	repository.contracts[contract.Hash] = contract
 	return nil
 }
 
@@ -43,10 +43,10 @@ func (repository *InMemory) ContractExists(contractHash string) bool {
 	return present
 }
 
-func (repository *InMemory) FindContract(contractHash string) *core.Contract {
+func (repository *InMemory) FindContract(contractHash string) (core.Contract, error) {
 	contract, ok := repository.contracts[contractHash]
 	if !ok {
-		return nil
+		return core.Contract{}, ErrContractDoesNotExist(contractHash)
 	}
 	for _, block := range repository.blocks {
 		for _, transaction := range block.Transactions {
@@ -55,13 +55,13 @@ func (repository *InMemory) FindContract(contractHash string) *core.Contract {
 			}
 		}
 	}
-	return contract
+	return contract, nil
 }
 
 func (repository *InMemory) MissingBlockNumbers(startingBlockNumber int64, endingBlockNumber int64) []int64 {
 	missingNumbers := []int64{}
 	for blockNumber := int64(startingBlockNumber); blockNumber <= endingBlockNumber; blockNumber++ {
-		if repository.blocks[blockNumber] == nil {
+		if _, ok := repository.blocks[blockNumber]; !ok {
 			missingNumbers = append(missingNumbers, blockNumber)
 		}
 	}
@@ -70,14 +70,14 @@ func (repository *InMemory) MissingBlockNumbers(startingBlockNumber int64, endin
 
 func NewInMemory() *InMemory {
 	return &InMemory{
-		blocks:    make(map[int64]*core.Block),
-		contracts: make(map[string]*core.Contract),
+		blocks:    make(map[int64]core.Block),
+		contracts: make(map[string]core.Contract),
 		logs:      make(map[string][]core.Log),
 	}
 }
 
 func (repository *InMemory) CreateBlock(block core.Block) error {
-	repository.blocks[block.Number] = &block
+	repository.blocks[block.Number] = block
 	return nil
 }
 
@@ -85,8 +85,11 @@ func (repository *InMemory) BlockCount() int {
 	return len(repository.blocks)
 }
 
-func (repository *InMemory) FindBlockByNumber(blockNumber int64) *core.Block {
-	return repository.blocks[blockNumber]
+func (repository *InMemory) FindBlockByNumber(blockNumber int64) (core.Block, error) {
+	if block, ok := repository.blocks[blockNumber]; ok {
+		return block, nil
+	}
+	return core.Block{}, ErrBlockDoesNotExist(blockNumber)
 }
 
 func (repository *InMemory) MaxBlockNumber() int64 {
diff --git a/pkg/repositories/postgres.go b/pkg/repositories/postgres.go
index 0d59b033..1f8cdf4d 100644
--- a/pkg/repositories/postgres.go
+++ b/pkg/repositories/postgres.go
@@ -7,6 +7,8 @@ import (
 
 	"errors"
 
+	"fmt"
+
 	"github.com/8thlight/vulcanizedb/pkg/config"
 	"github.com/8thlight/vulcanizedb/pkg/core"
 	"github.com/jmoiron/sqlx"
@@ -25,6 +27,28 @@ var (
 	ErrUnableToSetNode    = errors.New("postgres: unable to set node")
 )
 
+var ErrContractDoesNotExist = func(contractHash string) error {
+	return errors.New(fmt.Sprintf("Contract %v does not exist", contractHash))
+}
+
+var ErrBlockDoesNotExist = func(blockNumber int64) error {
+	return errors.New(fmt.Sprintf("Block number %d does not exist", blockNumber))
+}
+
+func NewPostgres(databaseConfig config.Database, node core.Node) (Postgres, error) {
+	connectString := config.DbConnectionString(databaseConfig)
+	db, err := sqlx.Connect("postgres", connectString)
+	if err != nil {
+		return Postgres{}, ErrDBConnectionFailed
+	}
+	pg := Postgres{Db: db, node: node}
+	err = pg.CreateNode(&node)
+	if err != nil {
+		return Postgres{}, ErrUnableToSetNode
+	}
+	return pg, nil
+}
+
 func (repository Postgres) CreateLogs(logs []core.Log) error {
 	tx, _ := repository.Db.BeginTx(context.Background(), nil)
 	for _, tlog := range logs {
@@ -71,20 +95,6 @@ func (repository Postgres) FindLogs(address string, blockNumber int64) []core.Lo
 	return repository.loadLogs(logRows)
 }
 
-func NewPostgres(databaseConfig config.Database, node core.Node) (Postgres, error) {
-	connectString := config.DbConnectionString(databaseConfig)
-	db, err := sqlx.Connect("postgres", connectString)
-	if err != nil {
-		return Postgres{}, ErrDBConnectionFailed
-	}
-	pg := Postgres{Db: db, node: node}
-	err = pg.CreateNode(&node)
-	if err != nil {
-		return Postgres{}, ErrUnableToSetNode
-	}
-	return pg, nil
-}
-
 func (repository *Postgres) CreateNode(node *core.Node) error {
 	var nodeId int64
 	err := repository.Db.QueryRow(
@@ -129,17 +139,17 @@ func (repository Postgres) ContractExists(contractHash string) bool {
 	return exists
 }
 
-func (repository Postgres) FindContract(contractHash string) *core.Contract {
+func (repository Postgres) FindContract(contractHash string) (core.Contract, error) {
 	var hash string
 	var abi string
 	contract := repository.Db.QueryRow(
 		`SELECT contract_hash, contract_abi FROM watched_contracts WHERE contract_hash=$1`, contractHash)
 	err := contract.Scan(&hash, &abi)
 	if err == sql.ErrNoRows {
-		return nil
+		return core.Contract{}, ErrContractDoesNotExist(contractHash)
 	}
 	savedContract := repository.addTransactions(core.Contract{Hash: hash, Abi: abi})
-	return &savedContract
+	return savedContract, nil
 }
 
 func (repository Postgres) MaxBlockNumber() int64 {
@@ -162,7 +172,7 @@ func (repository Postgres) MissingBlockNumbers(startingBlockNumber int64, highes
 	return numbers
 }
 
-func (repository Postgres) FindBlockByNumber(blockNumber int64) *core.Block {
+func (repository Postgres) FindBlockByNumber(blockNumber int64) (core.Block, error) {
 	blockRows, _ := repository.Db.Query(
 		`SELECT id,
                        block_number,
@@ -183,9 +193,9 @@ func (repository Postgres) FindBlockByNumber(blockNumber int64) *core.Block {
 		savedBlocks = append(savedBlocks, savedBlock)
 	}
 	if len(savedBlocks) > 0 {
-		return &savedBlocks[0]
+		return savedBlocks[0], nil
 	} else {
-		return nil
+		return core.Block{}, ErrBlockDoesNotExist(blockNumber)
 	}
 }
 
diff --git a/pkg/repositories/postgres_test.go b/pkg/repositories/postgres_test.go
index dca3f37f..eaef2d8a 100644
--- a/pkg/repositories/postgres_test.go
+++ b/pkg/repositories/postgres_test.go
@@ -43,11 +43,12 @@ var _ = Describe("Postgres repository", func() {
 		node := core.Node{GenesisBlock: "GENESIS", NetworkId: 1}
 		repository, _ := repositories.NewPostgres(cfg.Database, node)
 
-		err := repository.CreateBlock(badBlock)
-		savedBlock := repository.FindBlockByNumber(123)
+		err1 := repository.CreateBlock(badBlock)
+		savedBlock, err2 := repository.FindBlockByNumber(123)
 
-		Expect(err).ToNot(BeNil())
-		Expect(savedBlock).To(BeNil())
+		Expect(err1).To(HaveOccurred())
+		Expect(err2).To(HaveOccurred())
+		Expect(savedBlock).To(BeZero())
 	})
 
 	It("throws error when can't connect to the database", func() {
@@ -96,11 +97,12 @@ var _ = Describe("Postgres repository", func() {
 		node := core.Node{GenesisBlock: "GENESIS", NetworkId: 1}
 		repository, _ := repositories.NewPostgres(cfg.Database, node)
 
-		err := repository.CreateBlock(block)
-		savedBlock := repository.FindBlockByNumber(123)
+		err1 := repository.CreateBlock(block)
+		savedBlock, err2 := repository.FindBlockByNumber(123)
 
-		Expect(err).ToNot(BeNil())
-		Expect(savedBlock).To(BeNil())
+		Expect(err1).To(HaveOccurred())
+		Expect(err2).To(HaveOccurred())
+		Expect(savedBlock).To(BeZero())
 	})
 
 })
diff --git a/pkg/repositories/repository.go b/pkg/repositories/repository.go
index 51e0d81d..fe062989 100644
--- a/pkg/repositories/repository.go
+++ b/pkg/repositories/repository.go
@@ -5,12 +5,12 @@ import "github.com/8thlight/vulcanizedb/pkg/core"
 type Repository interface {
 	CreateBlock(block core.Block) error
 	BlockCount() int
-	FindBlockByNumber(blockNumber int64) *core.Block
+	FindBlockByNumber(blockNumber int64) (core.Block, error)
 	MaxBlockNumber() int64
 	MissingBlockNumbers(startingBlockNumber int64, endingBlockNumber int64) []int64
 	CreateContract(contract core.Contract) error
 	ContractExists(contractHash string) bool
-	FindContract(contractHash string) *core.Contract
+	FindContract(contractHash string) (core.Contract, error)
 	CreateLogs(log []core.Log) error
 	FindLogs(address string, blockNumber int64) []core.Log
 }
diff --git a/pkg/repositories/testing/helpers.go b/pkg/repositories/testing/helpers.go
index c482be68..d13bc29f 100644
--- a/pkg/repositories/testing/helpers.go
+++ b/pkg/repositories/testing/helpers.go
@@ -49,8 +49,8 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 			}
 			repositoryTwo := buildRepository(nodeTwo)
 
-			foundBlock := repositoryTwo.FindBlockByNumber(123)
-			Expect(foundBlock).To(BeNil())
+			_, err := repositoryTwo.FindBlockByNumber(123)
+			Expect(err).To(HaveOccurred())
 		})
 
 		It("saves the attributes of the block", func() {
@@ -79,7 +79,8 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 
 			repository.CreateBlock(block)
 
-			savedBlock := repository.FindBlockByNumber(blockNumber)
+			savedBlock, err := repository.FindBlockByNumber(blockNumber)
+			Expect(err).NotTo(HaveOccurred())
 			Expect(savedBlock.Difficulty).To(Equal(difficulty))
 			Expect(savedBlock.GasLimit).To(Equal(gasLimit))
 			Expect(savedBlock.GasUsed).To(Equal(gasUsed))
@@ -93,9 +94,9 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 		})
 
 		It("does not find a block when searching for a number that does not exist", func() {
-			savedBlock := repository.FindBlockByNumber(111)
+			_, err := repository.FindBlockByNumber(111)
 
-			Expect(savedBlock).To(BeNil())
+			Expect(err).To(HaveOccurred())
 		})
 
 		It("saves one transaction associated to the block", func() {
@@ -106,7 +107,7 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 
 			repository.CreateBlock(block)
 
-			savedBlock := repository.FindBlockByNumber(123)
+			savedBlock, _ := repository.FindBlockByNumber(123)
 			Expect(len(savedBlock.Transactions)).To(Equal(1))
 		})
 
@@ -118,7 +119,7 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 
 			repository.CreateBlock(block)
 
-			savedBlock := repository.FindBlockByNumber(123)
+			savedBlock, _ := repository.FindBlockByNumber(123)
 			Expect(len(savedBlock.Transactions)).To(Equal(2))
 		})
 
@@ -145,7 +146,7 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 
 			repository.CreateBlock(block)
 
-			savedBlock := repository.FindBlockByNumber(123)
+			savedBlock, _ := repository.FindBlockByNumber(123)
 			Expect(len(savedBlock.Transactions)).To(Equal(1))
 			savedTransaction := savedBlock.Transactions[0]
 			Expect(savedTransaction.Hash).To(Equal(transaction.Hash))
@@ -231,23 +232,23 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 		It("returns the contract when it exists", func() {
 			repository.CreateContract(core.Contract{Hash: "x123"})
 
-			contract := repository.FindContract("x123")
-			Expect(contract).NotTo(BeNil())
+			contract, err := repository.FindContract("x123")
+			Expect(err).NotTo(HaveOccurred())
 			Expect(contract.Hash).To(Equal("x123"))
 
 			Expect(repository.ContractExists("x123")).To(BeTrue())
 			Expect(repository.ContractExists("x456")).To(BeFalse())
 		})
 
-		It("returns nil if contract does not exist", func() {
-			contract := repository.FindContract("x123")
-			Expect(contract).To(BeNil())
+		It("returns err if contract does not exist", func() {
+			_, err := repository.FindContract("x123")
+			Expect(err).To(HaveOccurred())
 		})
 
 		It("returns empty array when no transactions 'To' a contract", func() {
 			repository.CreateContract(core.Contract{Hash: "x123"})
-			contract := repository.FindContract("x123")
-			Expect(contract).ToNot(BeNil())
+			contract, err := repository.FindContract("x123")
+			Expect(err).ToNot(HaveOccurred())
 			Expect(contract.Transactions).To(BeEmpty())
 		})
 
@@ -263,8 +264,8 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 			repository.CreateBlock(block)
 
 			repository.CreateContract(core.Contract{Hash: "x123"})
-			contract := repository.FindContract("x123")
-			Expect(contract).ToNot(BeNil())
+			contract, err := repository.FindContract("x123")
+			Expect(err).ToNot(HaveOccurred())
 			Expect(contract.Transactions).To(
 				Equal([]core.Transaction{
 					{Hash: "TRANSACTION1", To: "x123"},
@@ -277,8 +278,8 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 				Abi:  "{\"some\": \"json\"}",
 				Hash: "x123",
 			})
-			contract := repository.FindContract("x123")
-			Expect(contract).ToNot(BeNil())
+			contract, err := repository.FindContract("x123")
+			Expect(err).ToNot(HaveOccurred())
 			Expect(contract.Abi).To(Equal("{\"some\": \"json\"}"))
 		})
 
@@ -291,8 +292,8 @@ func AssertRepositoryBehavior(buildRepository func(node core.Node) repositories.
 				Abi:  "{\"some\": \"different json\"}",
 				Hash: "x123",
 			})
-			contract := repository.FindContract("x123")
-			Expect(contract).ToNot(BeNil())
+			contract, err := repository.FindContract("x123")
+			Expect(err).ToNot(HaveOccurred())
 			Expect(contract.Abi).To(Equal("{\"some\": \"different json\"}"))
 		})
 	})