Fix the cannot read property range of null bug

packages/sol-tracing-utils/CHANGELOG.json

@@ -17,6 +17,10 @@
             {
                 "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
             }
         ]
     },

packages/sol-tracing-utils/src/ast_visitor.ts

@@ -89,8 +89,10 @@ export class ASTVisitor {
         this._visitStatement(ast);
     }
     public ExpressionStatement(ast: Parser.ExpressionStatement): void {
+        if (!_.isNull(ast.expression)) {
             this._visitStatement(ast.expression);
         }
+    }
     public InlineAssemblyStatement(ast: Parser.InlineAssemblyStatement): void {
         this._visitStatement(ast);
     }