Fix deriveXAddress null behavior (#1964)

* Fix deriveXAddress null behavior

* Also check for undefined

* Simplify theTag

* Add test case for undefined

packages/ripple-address-codec/HISTORY.md

@@ -1,5 +1,8 @@
 # ripple-address-codec
 
+## Unreleased
+- Fixed `encodeXAddress` to handle `null` equivalently to `false`.
+
 ## 4.2.1 (2021-12-1)
 - Fix issue where npm < 7 could not install the library
 - Initial pass at linting this codebase with new rules

packages/ripple-address-codec/src/index.ts

@@ -43,8 +43,9 @@ function encodeXAddress(
   if (tag > MAX_32_BIT_UNSIGNED_INT) {
     throw new Error('Invalid tag')
   }
-  const theTag = tag === false ? 0 : tag
-  const flag = tag === false ? 0 : 1
+  const theTag = tag || 0
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition -- Passing null is a common js mistake
+  const flag = tag === false || tag == null ? 0 : 1
   /* eslint-disable no-bitwise ---
    * need to use bitwise operations here */
   const bytes = Buffer.concat([