Fixes issue introduced in v0.7.22

In some cases we want hex buffers to represent `0` with a 0-length
buffer, and in others we want it represented as a 1-byte buffer `00`

package.json

@@ -1,6 +1,6 @@
 {
   "name": "gridplus-sdk",
-  "version": "0.7.22",
+  "version": "0.7.23",
   "description": "SDK to interact with GridPlus Lattice1 device",
   "scripts": {
     "commit": "git-cz",

src/ethereum.js

@@ -428,10 +428,13 @@ function isBase10NumStr(x) {
 
 // Ensure a param is represented by a buffer
 // TODO: Remove circular dependency in util.js so that we can put this function there
-function ensureHexBuffer(x) {
+function ensureHexBuffer(x, zeroIsNull=true) {
   try {
-    // For null values, return a 0-sized buffer
-    if (x === null) return Buffer.alloc(0);
+    // For null values, return a 0-sized buffer. For most situations we assume
+    // 0 should be represented with a zero-length buffer (e.g. for RLP-building
+    // txs), but it can also be treated as a 1-byte buffer (`00`) if needed
+    if (x === null || (x === 0 && zeroIsNull === true)) 
+      return Buffer.alloc(0);
     const isNumber = typeof x === 'number' || isBase10NumStr(x);
     // Otherwise try to get this converted to a hex string
     if (isNumber) {
@@ -646,7 +649,8 @@ function parseEIP712Item(data, type, isEthers=false) {
       data = `0x${data.toString('hex')}`
     }
   } else if (type === 'uint8' || type === 'uint16' || type === 'uint32' || type === 'uint64') {
-    data = parseInt(ensureHexBuffer(data).toString('hex'), 16)
+    // In this case we want the hex buffer to represent `0` as a 1-byte buffer (`00`)
+    data = parseInt(ensureHexBuffer(data, false).toString('hex'), 16)
   } else if (type === 'uint256') {
     let b = ensureHexBuffer(data);
     // Edge case to handle 0-value bignums