diff --git a/doc.go b/doc.go
index 8e8d1f04..30780327 100644
--- a/doc.go
+++ b/doc.go
@@ -34,6 +34,7 @@ var (
 	errSerializeHashedNode    = errors.New("trying to serialize a hashed internal node")
 	errInsertIntoOtherStem    = errors.New("insert splits a stem where it should not happen")
 	errUnknownNodeType        = errors.New("unknown node type detected")
+	errNilNodeType            = errors.New("nil node type detected")
 	errMissingNodeInStateless = errors.New("trying to access a node that is missing from the stateless view")
 	errIsPOAStub              = errors.New("trying to read/write a proof of absence leaf node")
 )
diff --git a/tree.go b/tree.go
index 44d61c85..0c17dbd2 100644
--- a/tree.go
+++ b/tree.go
@@ -329,9 +329,14 @@ func (n *InternalNode) Children() []VerkleNode {
 
 // SetChild *replaces* the child at the given index with the given node.
 func (n *InternalNode) SetChild(i int, c VerkleNode) error {
+	if c == nil {
+		return errNilNodeType
+	}
+
 	if i >= NodeWidth {
 		return errors.New("child index higher than node width")
 	}
+
 	n.children[i] = c
 	return nil
 }
@@ -608,8 +613,14 @@ func (n *InternalNode) Delete(key []byte, resolver NodeResolverFn) (bool, error)
 			// signal that this node should be deleted
 			// as well.
 			for _, c := range n.children {
-				if _, ok := c.(Empty); !ok {
+				switch c.(type) {
+				case *InternalNode, *LeafNode:
 					break
+				case Empty, HashedNode:
+				case UnknownNode:
+					panic(errUnknownNodeType)
+				default:
+					panic(errNilNodeType)
 				}
 			}
 
@@ -639,14 +650,20 @@ func (n *InternalNode) Flush(flush NodeFlushFn) {
 
 	n.Commit()
 	for i, child := range n.children {
-		if c, ok := child.(*InternalNode); ok {
+		switch c := child.(type) {
+		case *InternalNode:
 			c.Commit()
 			c.Flush(flushAndCapturePath)
 			n.children[i] = HashedNode{}
-		} else if c, ok := child.(*LeafNode); ok {
+		case *LeafNode:
 			c.Commit()
-			flushAndCapturePath(c.stem[:n.depth+1], n.children[i])
+			flushAndCapturePath(c.stem[:n.depth+1], c)
 			n.children[i] = HashedNode{}
+		case Empty, HashedNode:
+		case UnknownNode:
+			panic(errUnknownNodeType)
+		default:
+			panic(errNilNodeType)
 		}
 	}
 	flush(path, n)
@@ -875,33 +892,32 @@ func (n *InternalNode) GetProofItems(keys keylist, resolver NodeResolverFn) (*Pr
 	var fiPtrs [NodeWidth]*Fr
 	var points [NodeWidth]*Point
 	for i, child := range n.children {
+		var c VerkleNode
+
 		fiPtrs[i] = &fi[i]
-		if child != nil {
-			var c VerkleNode
-			if _, ok := child.(HashedNode); ok {
-				childpath := make([]byte, n.depth+1)
-				copy(childpath[:n.depth+1], keys[0][:n.depth])
-				childpath[n.depth] = byte(i)
-				if resolver == nil {
-					return nil, nil, nil, fmt.Errorf("no resolver for path %x", childpath)
-				}
-				serialized, err := resolver(childpath)
-				if err != nil {
-					return nil, nil, nil, fmt.Errorf("error resolving for path %x: %w", childpath, err)
-				}
-				c, err = ParseNode(serialized, n.depth+1)
-				if err != nil {
-					return nil, nil, nil, err
-				}
-				n.children[i] = c
-			} else {
-				c = child
+		switch child := child.(type) {
+		case HashedNode:
+			childpath := make([]byte, n.depth+1)
+			copy(childpath[:n.depth+1], keys[0][:n.depth])
+			childpath[n.depth] = byte(i)
+			if resolver == nil {
+				return nil, nil, nil, fmt.Errorf("no resolver for path %x", childpath)
 			}
-			points[i] = c.Commitment()
-		} else {
-			// TODO: add a test case to cover this scenario.
-			points[i] = new(Point)
+			serialized, err := resolver(childpath)
+			if err != nil {
+				return nil, nil, nil, fmt.Errorf("error resolving for path %x: %w", childpath, err)
+			}
+			c, err = ParseNode(serialized, n.depth+1)
+			if err != nil {
+				return nil, nil, nil, err
+			}
+			n.children[i] = c
+		case *InternalNode, *LeafNode, Empty, UnknownNode:
+			c = child
+		default:
+			panic(errNilNodeType)
 		}
+		points[i] = c.Commitment()
 	}
 	if err := banderwagon.BatchMapToScalarField(fiPtrs[:], points[:]); err != nil {
 		return nil, nil, nil, fmt.Errorf("batch mapping to scalar fields: %s", err)
@@ -972,8 +988,14 @@ func (n *InternalNode) Serialize() ([]byte, error) {
 	// Write the <bitlist>.
 	bitlist := ret[internalBitlistOffset:internalCommitmentOffset]
 	for i, c := range n.children {
-		if _, ok := c.(Empty); !ok {
+		switch c.(type) {
+		case *InternalNode, *LeafNode:
 			setBit(bitlist, i)
+		case Empty, HashedNode:
+		case UnknownNode:
+			panic(errUnknownNodeType)
+		default:
+			panic(errNilNodeType)
 		}
 	}
 
@@ -995,6 +1017,9 @@ func (n *InternalNode) Copy() VerkleNode {
 	}
 
 	for i, child := range n.children {
+		if child == nil {
+			panic(errNilNodeType)
+		}
 		ret.children[i] = child.Copy()
 	}
 
@@ -1024,7 +1049,7 @@ func (n *InternalNode) toDot(parent, path string) string {
 
 	for i, child := range n.children {
 		if child == nil {
-			continue
+			panic(errNilNodeType)
 		}
 		ret = fmt.Sprintf("%s%s", ret, child.toDot(me, fmt.Sprintf("%s%02x", path, i)))
 	}
@@ -1719,6 +1744,11 @@ func (n *InternalNode) collectNonHashedNodes(list []VerkleNode, paths [][]byte,
 			copy(childpath, path)
 			childpath[len(path)] = byte(i)
 			list, paths = childNode.collectNonHashedNodes(list, paths, childpath)
+		case Empty, HashedNode:
+		case UnknownNode:
+			panic(errUnknownNodeType)
+		default:
+			panic(errNilNodeType)
 		}
 	}
 	return list, paths
@@ -1729,8 +1759,14 @@ func (n *InternalNode) serializeInternalWithUncompressedCommitment(pointsIdx map
 	serialized := make([]byte, nodeTypeSize+bitlistSize+banderwagon.UncompressedSize)
 	bitlist := serialized[internalBitlistOffset:internalCommitmentOffset]
 	for i, c := range n.children {
-		if _, ok := c.(Empty); !ok {
+		switch c.(type) {
+		case *InternalNode, *LeafNode:
 			setBit(bitlist, i)
+		case Empty, HashedNode:
+		case UnknownNode:
+			panic(errUnknownNodeType)
+		default:
+			panic(errNilNodeType)
 		}
 	}
 	serialized[nodeTypeOffset] = internalRLPType