Possible fix for #4485

include/nlohmann/detail/input/input_adapters.hpp

@@ -23,6 +23,7 @@
     #include <istream>  // istream
 #endif                  // JSON_NO_IO
 
+#include <nlohmann/detail/exceptions.hpp>
 #include <nlohmann/detail/iterators/iterator_traits.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/type_traits.hpp>
@@ -420,6 +421,10 @@ typename container_input_adapter_factory_impl::container_input_adapter_factory<C
 // Special cases with fast paths
 inline file_input_adapter input_adapter(std::FILE* file)
 {
+    if (file == nullptr)
+    {
+        JSON_THROW(parse_error::create(101, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
+    }
     return file_input_adapter(file);
 }
 
@@ -446,6 +451,10 @@ template < typename CharT,
                int >::type = 0 >
 contiguous_bytes_input_adapter input_adapter(CharT b)
 {
+    if (b == nullptr)
+    {
+        JSON_THROW(parse_error::create(101, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
+    }
     auto length = std::strlen(reinterpret_cast<const char*>(b));
     const auto* ptr = reinterpret_cast<const char*>(b);
     return input_adapter(ptr, ptr + length);

single_include/nlohmann/json.hpp

@@ -6233,6 +6233,8 @@ NLOHMANN_JSON_NAMESPACE_END
     #include <istream>  // istream
 #endif                  // JSON_NO_IO
 
+// #include <nlohmann/detail/exceptions.hpp>
+
 // #include <nlohmann/detail/iterators/iterator_traits.hpp>
 
 // #include <nlohmann/detail/macro_scope.hpp>
@@ -6633,6 +6635,10 @@ typename container_input_adapter_factory_impl::container_input_adapter_factory<C
 // Special cases with fast paths
 inline file_input_adapter input_adapter(std::FILE* file)
 {
+    if (file == nullptr)
+    {
+        JSON_THROW(parse_error::create(101, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
+    }
     return file_input_adapter(file);
 }
 
@@ -6659,6 +6665,10 @@ template < typename CharT,
                int >::type = 0 >
 contiguous_bytes_input_adapter input_adapter(CharT b)
 {
+    if (b == nullptr)
+    {
+        JSON_THROW(parse_error::create(101, 0, "attempting to parse an empty input; check that your input string or stream contains the expected JSON", nullptr));
+    }
     auto length = std::strlen(reinterpret_cast<const char*>(b));
     const auto* ptr = reinterpret_cast<const char*>(b);
     return input_adapter(ptr, ptr + length);

tests/src/unit-concepts.cpp

@@ -20,7 +20,6 @@ TEST_CASE("concepts")
         // a, b: values of type X: json
 
         // TABLE 96 - Container Requirements
-
         // X::value_type must return T
         CHECK((std::is_same<json::value_type, json>::value));
 

tests/src/unit-deserialization.cpp

@@ -361,6 +361,10 @@ TEST_CASE("deserialization")
                 "start_object()", "key(one)", "number_unsigned(1)",
                 "end_object()", "parse_error(29)"
             }));
+
+            const char* string = nullptr;
+            CHECK_THROWS_WITH_AS(_ = json::parse(string), "[json.exception.parse_error.101] parse error: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
+            CHECK_THROWS_WITH_AS(_ = json::parse(nullptr), "[json.exception.parse_error.101] parse error: attempting to parse an empty input; check that your input string or stream contains the expected JSON", json::parse_error&);
         }
 
         SECTION("operator<<")