diff --git a/sharding/collation.go b/sharding/collation.go
index 56dd826df..19f1b8d05 100644
--- a/sharding/collation.go
+++ b/sharding/collation.go
@@ -11,13 +11,21 @@ import (
 
 // Collation base struct.
 type Collation struct {
-	header       *CollationHeader
-	body         []byte
+	header *CollationHeader
+	// body represents the serialized blob of a collation's transactions.
+	body []byte
+	// transactions serves as a useful slice to store deserialized chunks from the
+	// collation's body. Every time this transactions slice is updated, the serialized
+	// body would need to be recalculated. This will be a useful property for proposers
+	// in our system.
 	transactions []*types.Transaction
 }
 
 // CollationHeader base struct.
 type CollationHeader struct {
+	// RLP decoding only works on exported properties of structs. In this case, we want
+	// to keep collation properties as read-only and only accessible through getters.
+	// We can accomplish this through this nested data property.
 	data collationHeaderData
 }
 
diff --git a/sharding/database/inmemory.go b/sharding/database/inmemory.go
index 26d672af7..0e2a5c44b 100644
--- a/sharding/database/inmemory.go
+++ b/sharding/database/inmemory.go
@@ -35,11 +35,15 @@ func (sb *ShardKV) Has(k common.Hash) bool {
 }
 
 // Put updates a key's value in the mapping.
-func (sb *ShardKV) Put(k common.Hash, v []byte) {
+func (sb *ShardKV) Put(k common.Hash, v []byte) error {
+	// there is no error in a simple setting of a value in a go map.
 	sb.kv[k] = v
+	return nil
 }
 
 // Delete removes the key and value from the mapping.
-func (sb *ShardKV) Delete(k common.Hash) {
+func (sb *ShardKV) Delete(k common.Hash) error {
+	// There is no return value for deleting a simple key in a go map.
 	delete(sb.kv, k)
+	return nil
 }
diff --git a/sharding/database/inmemory_test.go b/sharding/database/inmemory_test.go
index e21886e52..b994a6550 100644
--- a/sharding/database/inmemory_test.go
+++ b/sharding/database/inmemory_test.go
@@ -18,4 +18,10 @@ func Test_ShardKVGet(t *testing.T) {
 	if val == nil {
 		t.Errorf("no value stored for key")
 	}
+
+	hash2 := common.StringToHash("")
+	val2, err := kv.Get(hash2)
+	if err == nil {
+		t.Errorf("non-existent key should not have a value. key=%v, value=%v", hash2, val2)
+	}
 }
diff --git a/sharding/shard.go b/sharding/shard.go
index 1d6182c04..8a4edc710 100644
--- a/sharding/shard.go
+++ b/sharding/shard.go
@@ -12,8 +12,8 @@ import (
 type shardBackend interface {
 	Get(k common.Hash) ([]byte, error)
 	Has(k common.Hash) bool
-	Put(k common.Hash, val []byte)
-	Delete(k common.Hash)
+	Put(k common.Hash, val []byte) error
+	Delete(k common.Hash) error
 }
 
 // Shard base struct.
@@ -137,13 +137,17 @@ func (s *Shard) SetAvailability(chunkRoot *common.Hash, availability bool) error
 		if err != nil {
 			return fmt.Errorf("cannot RLP encode availability: %v", err)
 		}
-		s.shardDB.Put(key, enc)
+		if err := s.shardDB.Put(key, enc); err != nil {
+			return fmt.Errorf("cannot update shardDB: %v", err)
+		}
 	} else {
 		enc, err := rlp.EncodeToBytes(false)
 		if err != nil {
 			return fmt.Errorf("cannot RLP encode availability: %v", err)
 		}
-		s.shardDB.Put(key, enc)
+		if err := s.shardDB.Put(key, enc); err != nil {
+			return fmt.Errorf("cannot update shardDB: %v", err)
+		}
 	}
 	return nil
 }
@@ -156,7 +160,9 @@ func (s *Shard) SaveHeader(header *CollationHeader) error {
 	}
 
 	// Uses the hash of the header as the key.
-	s.shardDB.Put(header.Hash(), encoded)
+	if err := s.shardDB.Put(header.Hash(), encoded); err != nil {
+		return fmt.Errorf("cannot update shardDB: %v", err)
+	}
 	return nil
 }
 
@@ -167,7 +173,9 @@ func (s *Shard) SaveBody(body []byte) error {
 	// chunkRoot := getChunkRoot(body) using the blob algorithm utils.
 	// right now we will just take the raw keccak256 of the body until #92 is merged.
 	chunkRoot := common.BytesToHash(body)
-	s.shardDB.Put(chunkRoot, body)
+	if err := s.shardDB.Put(chunkRoot, body); err != nil {
+		return fmt.Errorf("cannot update shardDB: %v", err)
+	}
 	s.SetAvailability(&chunkRoot, true)
 	return nil
 }
@@ -200,7 +208,9 @@ func (s *Shard) SetCanonical(header *CollationHeader) error {
 	if err != nil {
 		return fmt.Errorf("cannot encode header: %v", err)
 	}
-	s.shardDB.Put(key, encoded)
+	if err := s.shardDB.Put(key, encoded); err != nil {
+		return fmt.Errorf("cannot update shardDB: %v", err)
+	}
 	return nil
 }