Fixed error "ambiguous overload for operator|" (fixes #1411)

extras/tests/MemberProxy/CMakeLists.txt

@@ -7,6 +7,7 @@ add_executable(MemberProxyTests
 	clear.cpp
 	compare.cpp
 	containsKey.cpp
+	or.cpp
 	remove.cpp
 	set.cpp
 	size.cpp

extras/tests/MemberProxy/or.cpp

@@ -0,0 +1,29 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+TEST_CASE("MemberProxy::operator|()") {
+  DynamicJsonDocument doc(4096);
+
+  SECTION("const char*") {
+    doc["a"] = "hello";
+
+    REQUIRE((doc["a"] | "world") == std::string("hello"));
+    REQUIRE((doc["b"] | "world") == std::string("world"));
+  }
+
+  SECTION("Issue #1411") {
+    doc["sensor"] = "gps";
+
+    const char *test = "test";  // <- the literal must be captured in a variable
+                                // to trigger the bug
+    const char *sensor = doc["sensor"] | test;  // "gps"
+
+    REQUIRE(sensor == std::string("gps"));
+  }
+}