diff --git a/src/utils.cc b/src/utils.cc
index b47ee2c..b5063ff 100644
--- a/src/utils.cc
+++ b/src/utils.cc
@@ -48,6 +48,9 @@
 }
 
 std::string PrettyDescriptor(const String* java_descriptor) {
+  if (java_descriptor == NULL) {
+    return "null";
+  }
   std::string descriptor(java_descriptor->ToModifiedUtf8());
 
   // Count the number of '['s to get the dimensionality.