'0x' strings returned by contract are incorrectly interpreted as nulls (#4730)

* 🐛 Fix decoding bug for the "0x" string

* 🎨 Update the validation check

* 🎨 Improve the condition to be more readable

* 📝 Update change log doc

Author: nazarhussain

CHANGELOG.md

@@ -507,6 +507,7 @@ Released with 1.0.0-beta.37 code base.
 -  Updated README to include Webpack 5 create-react-app support instructions (#4173)
 -  Update the documentation for `methods.myMethod.estimateGas` (#4702)
 -  Fix typos in REVIEW.md and TESTING.md (#4691)
+-  Fix encoding for "0x" string values (#4512)
 
 
 ### Changed

packages/web3-eth-abi/src/index.js

@@ -362,7 +362,12 @@ ABICoder.prototype.decodeParametersWith = function (outputs, bytes, loose) {
 
     outputs.forEach(function (output, i) {
         var decodedValue = res[returnValue.__length__];
-        decodedValue = (decodedValue === '0x') ? null : decodedValue;
+
+        const isStringObject = typeof output === 'object' && output.type && output.type === 'string';
+        const isStringType = typeof output === 'string' && output === 'string';
+
+        // only convert `0x` to null if it's not string value
+        decodedValue = (decodedValue === '0x' && !isStringObject && !isStringType) ? null : decodedValue;
 
         returnValue[i] = decodedValue;
 

packages/web3-eth-abi/types/tests/abi-coder-test.ts

@@ -327,6 +327,12 @@ abiCoder.decodeParameter(
     0000000000000000000000004e`
 );
 
+// $ExpectType { [key: string]: any; }
+abiCoder.decodeParameter(
+    'string',
+    '0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000023078000000000000000000000000000000000000000000000000000000000000'
+);
+
 // $ExpectError
 abiCoder.decodeParameter('uint256', [345]);
 // $ExpectError

test/abi.decodeParameter.js

@@ -635,6 +635,9 @@ describe('lib/solidity/coder', function () {
                         '0000000000000000000000000000000000000000000000000000000000000060' +
                         '0000000000000000000000000000000000000000000000000000000000000006' +
                         '737472696e670000000000000000000000000000000000000000000000000000'})
+
+        test( { types: ['string'], expected: ["0x"],
+                values: '0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000023078000000000000000000000000000000000000000000000000000000000000'})
     });
 });