Don't attempt to generate function description when the location of a stacktrace frame could not be determined

src/aggregrate-errors.js

@@ -142,13 +142,17 @@ module.exports = function aggregrateAndThrowErrors(errors) {
 		let detailLines = renderErrorList(errors);	
 		let frame = determineLocation();
 
-		let functionString = (frame.alias != null)
-			? `${frame.alias} [${frame.functionName}]`
-			: frame.functionName;
+		let locationString = asExpression(() => {
+			if (frame != null) {
+				let functionString = (frame.alias != null)
+					? `${frame.alias} [${frame.functionName}]`
+					: frame.functionName;
 
-		let locationString = (frame != null)
-			? `${highlightBold(functionString)} in ${highlightBold(frame.shortPath)}, at line ${highlightBold(frame.location.line)} (${frame.location.path})`
-			: dimBold(`(could not determine location)`);
+				return `${highlightBold(functionString)} in ${highlightBold(frame.shortPath)}, at line ${highlightBold(frame.location.line)} (${frame.location.path})`;
+			} else {
+				return dimBold(`(could not determine location)`);
+			}
+		});
 
 		return new AggregrateValidationError(`One or more validation errors occurred at ${locationString}:\n${detailLines}`, {
 			errors: errors