diff --git a/src/modules/graphic/ssggraph/grcarlight.h b/src/modules/graphic/ssggraph/grcarlight.h
index 930304b60..2c50ab55d 100644
--- a/src/modules/graphic/ssggraph/grcarlight.h
+++ b/src/modules/graphic/ssggraph/grcarlight.h
@@ -69,7 +69,7 @@ public:
 
   virtual const char *getTypeName(void)  { return ssgVtxTable::getTypeName();}
 
-  virtual void print ( FILE *fd = stderr, const char *indent = "", int how_much = 2) { ssgVtxTable::print(fd,const_cast<char*>(indent),how_much);}
+  virtual void print ( FILE *fd = stderr, const char *indent = nullptr, int how_much = 2) { ssgVtxTable::print(fd,const_cast<char*>(indent),how_much);}
   virtual int load ( FILE *fd )  {return  ssgVtxTable::load(fd);}
   virtual int save ( FILE *fd )  {return  ssgVtxTable::save(fd);}
 };
diff --git a/src/modules/graphic/ssggraph/grshadow.h b/src/modules/graphic/ssggraph/grshadow.h
index 2087f8a5b..27298bf32 100644
--- a/src/modules/graphic/ssggraph/grshadow.h
+++ b/src/modules/graphic/ssggraph/grshadow.h
@@ -45,7 +45,7 @@ public:
 
   virtual ~ssgVtxTableShadow (void);
   virtual const char *getTypeName(void)  { return ssgVtxTable::getTypeName();}
-  virtual void print ( FILE *fd = stderr, const char *indent = "", int how_much = 2) { ssgVtxTable::print(fd,const_cast<char*>(indent),how_much);}
+  virtual void print ( FILE *fd = stderr, const char *indent = nullptr, int how_much = 2) { ssgVtxTable::print(fd,const_cast<char*>(indent),how_much);}
   virtual int load ( FILE *fd )  {return  ssgVtxTable::load(fd);}
   virtual int save ( FILE *fd )  {return  ssgVtxTable::save(fd);}
 };
diff --git a/src/modules/graphic/ssggraph/grsmoke.h b/src/modules/graphic/ssggraph/grsmoke.h
index 5d0bb9e76..9831449e5 100644
--- a/src/modules/graphic/ssggraph/grsmoke.h
+++ b/src/modules/graphic/ssggraph/grsmoke.h
@@ -95,7 +95,7 @@ public:
 
     virtual const char *getTypeName(void)  { return ssgVtxTable::getTypeName();}
 
-    virtual void print ( FILE *fd = stderr, const char *indent = "", int how_much = 2) { ssgVtxTable::print(fd,const_cast<char*>(indent),how_much);}
+    virtual void print ( FILE *fd = stderr, const char *indent = nullptr, int how_much = 2) { ssgVtxTable::print(fd,const_cast<char*>(indent),how_much);}
     virtual int load ( FILE *fd )  {return  ssgVtxTable::load(fd);}
     virtual int save ( FILE *fd )  {return  ssgVtxTable::save(fd);}
 };
diff --git a/src/modules/graphic/ssggraph/grvertexarray.h b/src/modules/graphic/ssggraph/grvertexarray.h
index 2c3c89b7b..01bdb81a3 100644
--- a/src/modules/graphic/ssggraph/grvertexarray.h
+++ b/src/modules/graphic/ssggraph/grvertexarray.h
@@ -44,7 +44,7 @@ public:
 
   virtual const char *getTypeName(void) { return ssgVtxArray::getTypeName();}
 
-  virtual void print ( FILE *fd = stderr, char *indent = "", int how_much = 2 ) { ssgVtxArray::print(fd,indent,how_much);}
+  virtual void print ( FILE *fd = stderr, char *indent = nullptr, int how_much = 2 ) { ssgVtxArray::print(fd,indent,how_much);}
   virtual int load ( FILE *fd ) {return  ssgVtxArray::load(fd);}
   virtual int save ( FILE *fd ) {return  ssgVtxArray::save(fd);}
 } ;