4 files changed, 27 insertions, 3 deletions
diff --git a/packages/sol-tracing-utils/CHANGELOG.json b/packages/sol-tracing-utils/CHANGELOG.json
index 16a12ca63..89a5b6876 100644
--- a/packages/sol-tracing-utils/CHANGELOG.json
+++ b/packages/sol-tracing-utils/CHANGELOG.json
@@ -17,6 +17,14 @@
             {
                 "note": "Print resasonable error message on bytecode collision",
                 "pr": 1535
+            },
+            {
+                "note": "Fix the bug in `ASTVisitor` causing the 'cannot read property `range` of `null`' error",
+                "pr": 1557
+            },
+            {
+                "note": "Improve error messages when unable to find matching bytecode",
+                "pr": 1558
             }
         ]
     },
diff --git a/packages/sol-tracing-utils/package.json b/packages/sol-tracing-utils/package.json
index 4b0fff222..929c73b84 100644
--- a/packages/sol-tracing-utils/package.json
+++ b/packages/sol-tracing-utils/package.json
@@ -53,6 +53,7 @@
         "ethereum-types": "^1.1.6",
         "ethereumjs-util": "^5.1.1",
         "glob": "^7.1.2",
+        "chalk": "^2.3.0",
         "istanbul": "^0.4.5",
         "lodash": "^4.17.5",
         "loglevel": "^1.6.1",
diff --git a/packages/sol-tracing-utils/src/ast_visitor.ts b/packages/sol-tracing-utils/src/ast_visitor.ts
index 1ac9cd1de..27f19378b 100644
--- a/packages/sol-tracing-utils/src/ast_visitor.ts
+++ b/packages/sol-tracing-utils/src/ast_visitor.ts
@@ -89,7 +89,9 @@ export class ASTVisitor {
         this._visitStatement(ast);
     }
     public ExpressionStatement(ast: Parser.ExpressionStatement): void {
-        this._visitStatement(ast.expression);
+        if (!_.isNull(ast.expression)) {
+            this._visitStatement(ast.expression);
+        }
     }
     public InlineAssemblyStatement(ast: Parser.InlineAssemblyStatement): void {
         this._visitStatement(ast);
diff --git a/packages/sol-tracing-utils/src/trace_collector.ts b/packages/sol-tracing-utils/src/trace_collector.ts
index f5dde8762..2a1f15b83 100644
--- a/packages/sol-tracing-utils/src/trace_collector.ts
+++ b/packages/sol-tracing-utils/src/trace_collector.ts
@@ -1,4 +1,5 @@
 import { promisify } from '@0x/utils';
+import chalk from 'chalk';
 import { stripHexPrefix } from 'ethereumjs-util';
 import * as fs from 'fs';
 import { Collector } from 'istanbul';
@@ -71,9 +72,21 @@ export class TraceCollector {
             : (traceInfo as TraceInfoExistingContract).runtimeBytecode;
         const contractData = utils.getContractDataIfExists(this._contractsData, bytecode);
         if (_.isUndefined(contractData)) {
+            const shortenHex = (hex: string) => {
+                /**
+                 * Length chooses so that both error messages are of the same length
+                 * and it's enough data to figure out which artifact has a problem.
+                 */
+                const length = 18;
+                return `${hex.substr(0, length + 2)}...${hex.substr(hex.length - length, length)}`;
+            };
             const errMsg = isContractCreation
-                ? `Unknown contract creation transaction`
-                : `Transaction to an unknown address: ${traceInfo.address}`;
+                ? `Unable to find matching bytecode for contract creation ${chalk.bold(
+                      shortenHex(bytecode),
+                  )}, please check your artifacts. Ignoring...`
+                : `Unable to find matching bytecode for contract address ${chalk.bold(
+                      traceInfo.address,
+                  )}, please check your artifacts. Ignoring...`;
             this._logger.warn(errMsg);
             return;
         }