Fix crash when referencing non-existent target ref ID (#128)

The handleRefTargets function used Array.find() with a non-null assertion
to look up target references by refId. When a non-existent ref was
referenced (e.g., #Z when only #A and #B exist), find() returned
undefined and accessing .target on it caused a runtime TypeError.

This change adds proper error handling to throw a descriptive error
message that includes the invalid ref and lists all available refs,
making debugging much easier for users.

Author: Nepomuk5665

src/panels/graph.ts

@@ -158,8 +158,15 @@ function handleRefTargets(
 ): { targetFull?: string | undefined } {
     if (target.includes('#')) {
         const refs = getRefsFromTarget(target);
-        const findTargetByRefId = (targets: TargetObject[], refId: string) =>
-            targets.find((target) => target.refId === refId)!.target;
+        const findTargetByRefId = (targets: TargetObject[], refId: string) => {
+            const found = targets.find((target) => target.refId === refId);
+            if (!found) {
+                throw new Error(
+                    `Invalid target reference: #${refId} does not exist. Available refs: ${targets.map((t) => t.refId).join(', ')}`
+                );
+            }
+            return found.target;
+        };
 
         return {
             targetFull: refs.reduce(

test/panels/graph.test.js

@@ -142,3 +142,14 @@ test('graph should add other targets when a target contains refs', () => {
 
     expect(actualDivideTarget).toEqual(expectedDivideTarget);
 });
+
+test('graph should throw descriptive error when referencing non-existent target', () => {
+    expect(() => {
+        new Graph({
+            targets: [
+                'target-1',
+                "alias(divideSeries(#Z, #A), 'invalid ref')", // #Z doesn't exist
+            ],
+        });
+    }).toThrow(/Invalid target reference: #Z does not exist/);
+});