refactor to revertWithHex, and nil -> null

contracts/MIPSMemory.sol

@@ -19,17 +19,8 @@ contract MIPSMemory {
 
   mapping(bytes32 => Preimage) public preimage;
 
-  // TODO: can share code with getTrieNode
   function MissingPreimageRevert(bytes32 outhash, uint offset) internal pure {
-    bytes memory node = Lib_BytesUtils.toNibbles(abi.encodePacked(outhash, offset));
-    for (uint i = 0; i < node.length; i++) {
-      if (node[i] < bytes1(uint8(10))) {
-        node[i] = bytes1(uint8(node[i]) + uint8(0x30));
-      } else {
-        node[i] = bytes1(uint8(node[i]) + uint8(0x61-10));
-      }
-    }
-    revert(string(node));
+    Lib_BytesUtils.revertWithHex(abi.encodePacked(outhash, offset));
   }
 
   function GetPreimageLength(bytes32 outhash) public view returns (uint32) {

contracts/lib/Lib_BytesUtils.sol

@@ -253,6 +253,23 @@ library Lib_BytesUtils {
         return tempAddress;
     }
 
+    function revertWithHex(
+        bytes memory _bytes
+    )
+        internal
+        pure
+    {
+        bytes memory node = Lib_BytesUtils.toNibbles(_bytes);
+        for (uint i = 0; i < node.length; i++) {
+        if (node[i] < bytes1(uint8(10))) {
+            node[i] = bytes1(uint8(node[i]) + uint8(0x30));
+        } else {
+            node[i] = bytes1(uint8(node[i]) + uint8(0x61-10));
+        }
+        }
+        revert(string(node));
+    }
+
     function toNibbles(
         bytes memory _bytes
     )

contracts/lib/Lib_MerkleTrie.sol

@@ -103,15 +103,7 @@ library Lib_MerkleTrie {
     function getTrieNode(bytes32 nodeId) private view returns (TrieNode memory) {
         bytes memory encoded = GetTrie()[nodeId];
         if (encoded.length == 0) {
-            bytes memory node = Lib_BytesUtils.toNibbles(abi.encodePacked(nodeId));
-            for (uint i = 0; i < node.length; i++) {
-                if (node[i] < bytes1(uint8(10))) {
-                    node[i] = bytes1(uint8(node[i]) + uint8(0x30));
-                } else {
-                    node[i] = bytes1(uint8(node[i]) + uint8(0x61-10));
-                }
-            }
-            revert(string(node));
+            Lib_BytesUtils.revertWithHex(abi.encodePacked(nodeId));
         }
         require(keccak256(encoded) == nodeId, "bad hash in trie lookup");
         return getRawNode(encoded);

test/mips_test_execwtrie_dynamic.js

@@ -56,7 +56,7 @@ describe("Exec with trie dynamic", function () {
   it("add should work", async function () {
     let root = trieAdd['root']
     for (let i = 0; i < 12; i++) {
-      root = await dynamicExecWithTrie(c, m, mm, root, trieAdd['preimages'], nil)
+      root = await dynamicExecWithTrie(c, m, mm, root, trieAdd['preimages'], null)
       console.log(i, root)
     }
   })