diff --git a/libdevcore/CommonJS.cpp b/libdevcore/CommonJS.cpp
index 8d8638da5..9dc04b7e7 100644
--- a/libdevcore/CommonJS.cpp
+++ b/libdevcore/CommonJS.cpp
@@ -87,22 +87,22 @@ std::string fromRaw(h256 _n, unsigned* _inc)
 		std::string s((char const*)_n.data(), 32);
 		auto l = s.find_first_of('\0');
 		if (!l)
-			return NULL;
+			return "";
 		if (l != std::string::npos)
 		{
 			auto p = s.find_first_not_of('\0', l);
 			if (!(p == std::string::npos || (_inc && p == 31)))
-				return NULL;
+				return "";
 			if (_inc)
 				*_inc = (byte)s[31];
 			s.resize(l);
 		}
 		for (auto i: s)
 			if (i < 32)
-				return NULL;
+				return "";
 		return s;
 	}
-	return NULL;
+	return "";
 }
 
 Address fromString(std::string _sn)