--- src/regexstr.cpp.orig	2020-04-09 18:02:12 UTC

+++ src/regexstr.cpp

@@ -11,10 +11,16 @@ RegexStr RegexStr::fromStr(const std::st

 {

     RegexStr r;

     r.source_ = source;

-    try {

-        r.regex_ = std::regex(source, std::regex::extended);

-    }  catch (const std::exception& e) {

-        throw std::invalid_argument(e.what());

+    // An empty regex is not allowed in the POSIX grammar

+    // as one can infer from the grammar at

+    // https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_05_03

+    // => So we must not compile "" to a regex

+    if (!source.empty()) {

+        try {

+            r.regex_ = std::regex(source, std::regex::extended);

+        }  catch (const std::exception& e) {

+            throw std::invalid_argument(e.what());

+        }

     }

     return r;

 }

@@ -26,7 +32,11 @@ bool RegexStr::operator==(const RegexStr

 bool RegexStr::matches(const std::string& str) const

 {

-    return std::regex_match(str, regex_);

+    if (source_.empty()) {

+        return false;

+    } else {

+        return std::regex_match(str, regex_);

+    }

 }

 template<> RegexStr Converter<RegexStr>::parse(const std::string& source) {