fix: throw error instead of returning undefined

`rmPrefix()` now throws an error if the given code wasn't found.
This should make increase the usability of this module.

src/index.js

@@ -59,6 +59,9 @@ exports.rmPrefix = (data) => {
 exports.getCodec = (prefixedData) => {
   const code = util.varintBufferDecode(prefixedData)
   const codecName = codeToCodecName[code.toString('hex')]
+  if (codecName === undefined) {
+    throw new Error('Code `0x' + code.toString('hex') + '` not found')
+  }
   return codecName
 }
 

test/multicodec.spec.js

@@ -41,4 +41,16 @@ describe('multicodec', () => {
       'Codec `this-codec-doesnt-exist` not found'
     )
   })
+
+  it('throws error on unknown codec name when getting the codec', () => {
+    const code = Buffer.from('ffee', 'hex')
+
+    const buf = Buffer.from('hey')
+    const prefixedBuf = multicodec.addPrefix(code, buf)
+    expect(() => {
+      multicodec.getCodec(prefixedBuf)
+    }).to.throw(
+      'Code `0xffee` not found'
+    )
+  })
 })