fix: reject loadImage when src is null or invalid

Description:
- To handle non-string/non-Buffer sources while fetching image.
- Add test cases for '', null, and undefined inputs to loadImage()

Test Result:
```
npm run test
...
      ✔ rejects when loadImage is called with null
      ✔ rejects when loadImage is called with undefined
      ✔ rejects when loadImage is called with empty string

  291 passing (302ms)
  6 pending
```

Author: Ian-I-Chien

CHANGELOG.md

@@ -11,6 +11,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 ### Fixed
 * `roundRect()` shape incorrect when radii were large relative to rectangle size (#2400)
+* Reject loadImage when src is null or invalid (#2304)
 
 3.2.0
 ==================

lib/image.js

@@ -63,6 +63,10 @@ Object.defineProperty(Image.prototype, 'src', {
       }
     } else if (Buffer.isBuffer(val)) {
       setSource(this, val)
+    } else {
+      const err = new Error("Invalid image source")
+      if (typeof this.onerror === 'function') this.onerror(err)
+      else throw err
     }
   },
 

test/image.test.js

@@ -516,6 +516,24 @@ describe('Image', function () {
       img.src = path.join(bmpDir, 'bomb.bmp')
     })
 
+    it('rejects when loadImage is called with null', async function () {
+        await assert.rejects(
+            loadImage(null),
+        )
+    })
+
+    it('rejects when loadImage is called with undefined', async function () {
+        await assert.rejects(
+            loadImage(undefined),
+        )
+    })
+
+    it('rejects when loadImage is called with empty string', async function () {
+        await assert.rejects(
+            loadImage(''),
+        )
+    })
+
     function testImgd (img, data) {
       const ctx = createCanvas(img.width, img.height).getContext('2d')
       ctx.drawImage(img, 0, 0)