diff --git a/include/sta/Property.hh b/include/sta/Property.hh
index cd8eb1e5..047e3d1f 100644
--- a/include/sta/Property.hh
+++ b/include/sta/Property.hh
@@ -85,7 +85,7 @@ public:
   Type type() const { return type_; }
   const Unit *unit() const { return unit_; }
 
-  const char *asString(const Network *network) const;
+  std::string to_string(const Network *network) const;
   const char *stringValue() const; // valid for type string
   float floatValue() const;        // valid for type float
   bool boolValue() const;          // valid for type bool
diff --git a/sdc/Sdc.i b/sdc/Sdc.i
index 81d94240..8eabec89 100644
--- a/sdc/Sdc.i
+++ b/sdc/Sdc.i
@@ -1227,12 +1227,13 @@ filter_objects(const char *property,
     bool not_pattern_match = stringEq(op, "!~");
     for (T *object : *objects) {
       PropertyValue value(getProperty(object, property, sta));
-      const char *prop = value.asString(sta->network());
-      if (prop &&
-          ((exact_match && stringEq(prop, pattern))
-           || (not_match && !stringEq(prop, pattern))
-           || (pattern_match && patternMatch(pattern, prop))
-           || (not_pattern_match && !patternMatch(pattern, prop))))
+      string prop_str = value.to_string(sta->network());
+      const char *prop = prop_str.c_str();
+      if (!prop_str.empty()
+          && ((exact_match && stringEq(prop, pattern))
+              || (not_match && !stringEq(prop, pattern))
+              || (pattern_match && patternMatch(pattern, prop))
+              || (not_pattern_match && !patternMatch(pattern, prop))))
         filtered_objects.push_back(object);
     }
     delete objects;
diff --git a/search/Property.cc b/search/Property.cc
index 9c3f598a..85c3978f 100644
--- a/search/Property.cc
+++ b/search/Property.cc
@@ -613,8 +613,8 @@ PropertyValue::operator=(PropertyValue &&value)
   return *this;
 }
 
-const char *
-PropertyValue::asString(const Network *network) const
+string
+PropertyValue::to_string(const Network *network) const
 {
   switch (type_) {
   case Type::type_string:
@@ -652,9 +652,9 @@ PropertyValue::asString(const Network *network) const
   case Type::type_clks:
   case Type::type_paths:
   case Type::type_pwr_activity:
-    return nullptr;
+    return "";
   }
-  return nullptr;
+  return "";
 }
 
 const char *