Treat explicit nil as implicit nil

Field values should not behave differently depending on whether they were ommited from the initial create call.

client/document.go

@@ -697,7 +697,12 @@ func (doc *Document) Values() map[Field]*FieldValue {
 
 // Bytes returns the document as a serialzed byte array using CBOR encoding.
 func (doc *Document) Bytes() ([]byte, error) {
-	docMap, err := doc.toMap()
+	// We want to ommit properties with nil values from the map, as setting a
+	// propery to nil should result in the same serialized value as ommiting the
+	// the property from the document.
+	//
+	// This is particularly important for docID generation.
+	docMap, err := doc.toMap(true)
 	if err != nil {
 		return nil, err
 	}
@@ -713,7 +718,7 @@ func (doc *Document) Bytes() ([]byte, error) {
 // Note: This representation should not be used for any cryptographic operations,
 // such as signatures, or hashes as it does not guarantee canonical representation or ordering.
 func (doc *Document) String() (string, error) {
-	docMap, err := doc.toMap()
+	docMap, err := doc.toMap(false)
 	if err != nil {
 		return "", err
 	}
@@ -734,7 +739,7 @@ func (doc *Document) ToMap() (map[string]any, error) {
 // ToJSONPatch returns a json patch that can be used to update
 // a document by calling SetWithJSON.
 func (doc *Document) ToJSONPatch() ([]byte, error) {
-	docMap, err := doc.toMap()
+	docMap, err := doc.toMap(false)
 	if err != nil {
 		return nil, err
 	}
@@ -758,9 +763,11 @@ func (doc *Document) Clean() {
 	}
 }
 
-// converts the document into a map[string]any
-// including any sub documents
-func (doc *Document) toMap() (map[string]any, error) {
+// converts the document into a map[string]any including any sub documents.
+//
+// If `true` is provided, properties with nil values will be ommited from
+// the result.
+func (doc *Document) toMap(excludeEmpty bool) (map[string]any, error) {
 	doc.mu.RLock()
 	defer doc.mu.RUnlock()
 	docMap := make(map[string]any)
@@ -770,9 +777,13 @@ func (doc *Document) toMap() (map[string]any, error) {
 			return nil, NewErrFieldNotExist(v.Name())
 		}
 
+		if excludeEmpty && value.Value() == nil {
+			continue
+		}
+
 		if value.IsDocument() {
 			subDoc := value.Value().(*Document)
-			subDocMap, err := subDoc.toMap()
+			subDocMap, err := subDoc.toMap(excludeEmpty)
 			if err != nil {
 				return nil, err
 			}

internal/core/crdt/lwwreg.go

@@ -144,9 +144,20 @@ func (reg LWWRegister) setValue(ctx context.Context, val []byte, priority uint64
 		}
 	}
 
-	err = reg.store.Put(ctx, key.ToDS(), val)
-	if err != nil {
-		return NewErrFailedToStoreValue(err)
+	if len(val) <= 1 {
+		// If len(val) is 1 or less the property is nil and there is no reason for
+		// the field datastore key to exist.  Ommiting the key saves space and is
+		// consistent with what would be found if the user omitted the property on
+		// create.
+		err = reg.store.Delete(ctx, key.ToDS())
+		if err != nil {
+			return err
+		}
+	} else {
+		err = reg.store.Put(ctx, key.ToDS(), val)
+		if err != nil {
+			return NewErrFailedToStoreValue(err)
+		}
 	}
 
 	return reg.setPriority(ctx, reg.key, priority)

tests/integration/mutation/create/field_kinds/one_to_one/with_null_value_test.go

@@ -52,7 +52,31 @@ func TestMutationCreateOneToOne_WithExplicitNullOnPrimarySide(t *testing.T) {
 					"name":      "Will Ferguson",
 					"published": testUtils.NewDocIndex(0, 0),
 				},
-				ExpectedError: "target document is already linked to another document",
+			},
+			testUtils.Request{
+				Request: `
+					query {
+						Book {
+							name
+							author {
+								name
+							}
+						}
+					}`,
+				Results: map[string]any{
+					"Book": []map[string]any{
+						{
+							"name":   "Secrets at Maple Syrup Farm",
+							"author": nil,
+						},
+						{
+							"name": "How to Be a Canadian",
+							"author": map[string]any{
+								"name": "Will Ferguson",
+							},
+						},
+					},
+				},
 			},
 		},
 	}

tests/integration/mutation/create/with_null_value_test.go

@@ -13,11 +13,19 @@ package create
 import (
 	"testing"
 
+	"github.com/sourcenetwork/immutable"
+
 	testUtils "github.com/sourcenetwork/defradb/tests/integration"
 )
 
 func TestMutationCreate_WithOmittedValueAndExplicitNullValue(t *testing.T) {
 	test := testUtils.TestCase{
+		SupportedMutationTypes: immutable.Some([]testUtils.MutationType{
+			// Collection.Save would treat the second create as an update, and so
+			// is excluded from this test.
+			testUtils.CollectionNamedMutationType,
+			testUtils.GQLRequestMutationType,
+		}),
 		Actions: []any{
 			testUtils.SchemaUpdate{
 				Schema: `
@@ -37,28 +45,7 @@ func TestMutationCreate_WithOmittedValueAndExplicitNullValue(t *testing.T) {
 					"name": "John",
 					"age": null
 				}`,
-			},
-			testUtils.Request{
-				Request: `
-					query {
-						Users {
-							name
-							age
-						}
-					}
-				`,
-				Results: map[string]any{
-					"Users": []map[string]any{
-						{
-							"name": "John",
-							"age":  nil,
-						},
-						{
-							"name": "John",
-							"age":  nil,
-						},
-					},
-				},
+				ExpectedError: "a document with the given ID already exist",
 			},
 		},
 	}