Add default relationship color to handle old versions

Issue : #651

Author: Red-Hide

src/components/EditorCanvas/Relationship.jsx

@@ -1,5 +1,10 @@
 import { useMemo, useRef, useState, useEffect } from "react";
-import { Cardinality, ObjectType, Tab } from "../../data/constants";
+import {
+  Cardinality,
+  defaultBlue,
+  ObjectType,
+  Tab,
+} from "../../data/constants";
 import { calcPath } from "../../utils/calcPath";
 import { useDiagram, useSettings, useLayout, useSelect } from "../../hooks";
 import { useTranslation } from "react-i18next";
@@ -127,7 +132,7 @@ export default function Relationship({ data }) {
           className="relationship-path"
           fill="none"
           cursor="pointer"
-          style={{ stroke: data.color }}
+          style={{ stroke: data.color ?? defaultBlue }}
         />
         {settings.showRelationshipLabels && (
           <text

src/components/EditorSidePanel/RelationshipsTab/RelationshipInfo.jsx

@@ -17,6 +17,7 @@ import {
   Constraint,
   Action,
   ObjectType,
+  defaultBlue,
 } from "../../../data/constants";
 import { useDiagram, useLayout, useUndoRedo } from "../../../hooks";
 import i18n from "../../../i18n/i18n";
@@ -41,7 +42,7 @@ export default function RelationshipInfo({ data }) {
   const { t } = useTranslation();
   const { layout } = useLayout();
   const [editField, setEditField] = useState({});
-  const initialColorRef = useRef(data.color);
+  const initialColorRef = useRef(data.color ?? defaultBlue);
 
 
   const relValues = useMemo(() => {
@@ -215,7 +216,7 @@ export default function RelationshipInfo({ data }) {
           <ColorPicker
           usePopover={true}
           readOnly={layout.readOnly}
-          value={data.color}
+          value={data.color ?? defaultBlue}
           onChange={(color) => updateRelationship(data.id, { color })}
           onColorPick={(color) => handleColorPick(color)}
           />