Fix #124 by allowing an empty object for Usage#add method

Author: seratch

packages/agents-core/src/usage.ts

@@ -61,8 +61,14 @@ export class Usage {
     this.inputTokens += newUsage.inputTokens;
     this.outputTokens += newUsage.outputTokens;
     this.totalTokens += newUsage.totalTokens;
-    this.inputTokensDetails.push(...newUsage.inputTokensDetails);
-    this.outputTokensDetails.push(...newUsage.outputTokensDetails);
+    if (newUsage.inputTokensDetails) {
+      // The type does not allow unddefined, but it could happen runtime
+      this.inputTokensDetails.push(...newUsage.inputTokensDetails);
+    }
+    if (newUsage.outputTokensDetails) {
+      // The type does not allow unddefined, but it could happen runtime
+      this.outputTokensDetails.push(...newUsage.outputTokensDetails);
+    }
   }
 }
 

packages/agents-core/test/usage.test.ts

@@ -46,4 +46,11 @@ describe('Usage', () => {
     expect(usageA.outputTokens).toBe(5); // 1 + 4
     expect(usageA.totalTokens).toBe(9); // 2 + 7
   });
+
+  it('the add method accepts an empty object', () => {
+    const usage = new Usage({});
+    usage.add({} as Usage);
+    expect(usage.inputTokensDetails).toEqual([]);
+    expect(usage.outputTokensDetails).toEqual([]);
+  });
 });