fix: edge case constructing from string '0' (#121)

* fix: edge case constructing from string '0'

packages/ripple-binary-codec/src/types/uint-64.ts

@@ -54,6 +54,10 @@ class UInt64 extends UInt {
     }
 
     if (typeof val === "string") {
+      if (val === "0") {
+        return UInt64.from(0);
+      }
+
       if (!HEX_REGEX.test(val)) {
         throw new Error(`${val} is not a valid hex-string`);
       }

packages/ripple-binary-codec/test/uint.test.js

@@ -1,6 +1,32 @@
 const { coreTypes } = require("../dist/types");
 const { UInt8, UInt64 } = coreTypes;
 
+const { encode } = require("../dist");
+
+const binary =
+  "11007222000300003700000000000000003800000000000000006280000000000000000000000000000000000000005553440000000000000000000000000000000000000000000000000166D5438D7EA4C680000000000000000000000000005553440000000000AE123A8556F3CF91154711376AFB0F894F832B3D67D5438D7EA4C680000000000000000000000000005553440000000000F51DFC2A09D62CBBA1DFBDD4691DAC96AD98B90F";
+const json = {
+  Balance: {
+    currency: "USD",
+    issuer: "rrrrrrrrrrrrrrrrrrrrBZbvji",
+    value: "0",
+  },
+  Flags: 196608,
+  HighLimit: {
+    currency: "USD",
+    issuer: "rPMh7Pi9ct699iZUTWaytJUoHcJ7cgyziK",
+    value: "1000",
+  },
+  HighNode: "0",
+  LedgerEntryType: "RippleState",
+  LowLimit: {
+    currency: "USD",
+    issuer: "rG1QQv2nh2gr7RCZ1P8YYcBUKCCN633jCn",
+    value: "1000",
+  },
+  LowNode: "0",
+};
+
 test("compareToTests[0]", () => {
   expect(UInt8.from(124).compareTo(UInt64.from(124))).toBe(0);
 });
@@ -33,6 +59,11 @@ test("compareToTest[7]", () => {
   expect(UInt8.from(124).compareTo(13)).toBe(1);
 });
 
+test("UInt64 from string zero", () => {
+  expect(UInt64.from("0")).toEqual(UInt64.from(0));
+  expect(encode(json)).toEqual(binary);
+});
+
 test("valueOfTests", () => {
   let val = UInt8.from(1);
   val |= 0x2;