refactor: Use nullptr (c++11) instead of NULL

Regenerate univalue_escapes.h

Author: mxaddict

gen/gen.cpp

@@ -45,7 +45,7 @@ static void outputEscape()
 
 	for (unsigned int i = 0; i < 256; i++) {
 		if (escapes[i].empty()) {
-			printf("\tNULL,\n");
+			printf("\tnullptr,\n");
 		} else {
 			printf("\t\"");
 

lib/univalue.cpp

@@ -228,7 +228,7 @@ const char *uvTypeName(UniValue::VType t)
     }
 
     // not reached
-    return NULL;
+    return nullptr;
 }
 
 const UniValue& find_value(const UniValue& obj, const std::string& name)