fix(utils): do not fill empty records

follow up of: #466, prevent unset
records to be filled with empty tables: {}

kong/utils.go

@@ -355,7 +355,10 @@ func fillConfigRecord(schema gjson.Result, config Configuration, opts FillRecord
 				fieldConfig = subConfig.(map[string]interface{})
 			}
 			newSubConfig := fillConfigRecord(value.Get(fname), fieldConfig, opts)
-			res[fname] = map[string]interface{}(newSubConfig)
+			// when we are not filling defaults, only assign the subconfig when it's not empty
+			if opts.FillDefaults || len(newSubConfig) > 0 {
+				res[fname] = map[string]interface{}(newSubConfig)
+			}
 			return true
 		}
 

kong/utils_test.go

@@ -1971,6 +1971,48 @@ const fillConfigRecordTestSchemaWithAutoFields = `{
 }
 `
 
+const fillConfigRecordTestSchemaWithRecord = `{
+	"fields": {
+		"config": {
+			"type": "record",
+			"fields": [
+				{
+					"some_record": {
+							"required": true,
+              "fields": [
+                {
+                  "some_field": {
+                    "default": "kong",
+                    "type": "string"
+                  }
+                }
+              ],
+              "type": "record"
+          }
+				},
+				{
+					"some_other_record": {
+              "fields": [
+                {
+                  "some_field": {
+                    "type": "string"
+                  }
+                }
+              ],
+              "type": "record"
+          }
+				},
+				{
+					"string_1": {
+						"type": "string",
+					}
+				}
+			]
+		}
+	}
+}
+`
+
 func Test_fillConfigRecord_shorthand_fields(t *testing.T) {
 	tests := []struct {
 		name     string
@@ -2098,6 +2140,20 @@ func Test_fillConfigRecord_auto_only(t *testing.T) {
 				// defalt_string missing
 			},
 		},
+		{
+			name:   "not passing record field leaves field unset",
+			schema: gjson.Parse(fillConfigRecordTestSchemaWithRecord),
+			config: Configuration{
+				// some_record missing
+				"some_other_record": map[string]any{}, // explicitly set to empty record
+				"string_1":          "abc",
+			},
+			expected: Configuration{
+				// some_record was not filled
+				"some_other_record": map[string]any{}, // empty record remained unchanged
+				"string_1":          "abc",
+			},
+		},
 	}
 
 	for _, tc := range tests {