diff --git a/hotspot/src/share/vm/services/diagnosticArgument.cpp b/hotspot/src/share/vm/services/diagnosticArgument.cpp
index 0a1c20d8a2c..51126f063b4 100644
--- a/hotspot/src/share/vm/services/diagnosticArgument.cpp
+++ b/hotspot/src/share/vm/services/diagnosticArgument.cpp
@@ -61,7 +61,7 @@ void GenDCmdArgument::to_string(MemorySizeArgument m, char* buf, size_t len) {
 }
 
 void GenDCmdArgument::to_string(char* c, char* buf, size_t len) {
-  jio_snprintf(buf, len, "%s", c);
+  jio_snprintf(buf, len, "%s", (c != NULL) ? c : "");
 }
 
 void GenDCmdArgument::to_string(StringArrayArgument* f, char* buf, size_t len) {