Adding more explicit nullable types

src/LightningDB.Tests/DatabaseTests.cs

@@ -203,7 +203,7 @@ public void can_get_database_flags()
         // Test default database (should have no special flags)
         using (var txn = env.BeginTransaction())
         {
-            using var db = txn.OpenDatabase(null, new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create });
+            using var db = txn.OpenDatabase(new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create });
 
             var flags = db.GetFlags(txn);
             flags.ShouldBe(DatabaseOpenFlags.None);

src/LightningDB.Tests/EnvironmentTests.cs

@@ -115,7 +115,7 @@ public void can_put_multiple_key_value_pairs_and_flush_successfully()
         env.Open();
 
         using var tx = env.BeginTransaction();
-        using var db = tx.OpenDatabase(null, new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create });
+        using var db = tx.OpenDatabase(new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create });
 
         for (int i = 0; i < 5; i++)
         {
@@ -250,7 +250,7 @@ public void can_copy_to_file_stream()
 
         // Add some data to the source environment
         using (var tx = sourceEnv.BeginTransaction())
-        using (var db = tx.OpenDatabase(null, new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create }))
+        using (var db = tx.OpenDatabase(new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create }))
         {
             for (int i = 0; i < 5; i++)
             {
@@ -263,7 +263,7 @@ public void can_copy_to_file_stream()
         var tempFilePath = Path.Combine(TempPath(), "env_copy.mdb");
 
         // Ensure directory exists
-        Directory.CreateDirectory(Path.GetDirectoryName(tempFilePath));
+        Directory.CreateDirectory(Path.GetDirectoryName(tempFilePath)!);
 
         // Create a FileStream to the destination file
         using (var fileStream = new FileStream(tempFilePath, FileMode.Create, FileAccess.ReadWrite))
@@ -286,7 +286,7 @@ public void can_copy_with_compaction_to_file_stream()
 
         // Add some data to the source environment and then delete half of it to create free space
         using (var tx = sourceEnv.BeginTransaction())
-        using (var db = tx.OpenDatabase(null, new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create }))
+        using (var db = tx.OpenDatabase(new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create }))
         {
             for (int i = 0; i < 10; i++)
             {
@@ -310,7 +310,7 @@ public void can_copy_with_compaction_to_file_stream()
         var tempFilePath = Path.Combine(TempPath(), "env_copy_compact.mdb");
 
         // Ensure directory exists
-        Directory.CreateDirectory(Path.GetDirectoryName(tempFilePath));
+        Directory.CreateDirectory(Path.GetDirectoryName(tempFilePath)!);
 
         // Create a FileStream to the destination file
         using (var fileStream = new FileStream(tempFilePath, FileMode.Create, FileAccess.ReadWrite))
@@ -333,7 +333,7 @@ public void can_get_environment_file_stream()
 
         // Add some data to make sure the file has content
         using (var tx = env.BeginTransaction())
-        using (var db = tx.OpenDatabase(null, new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create }))
+        using (var db = tx.OpenDatabase(new DatabaseConfiguration { Flags = DatabaseOpenFlags.Create }))
         {
             tx.Put(db, "testkey", "testvalue");
             tx.Commit();
@@ -360,8 +360,8 @@ public void stream_throws_exception_for_null_argument()
         using var env = CreateEnvironment();
         env.Open();
 
-        // Null FileStream
-        Should.Throw<ArgumentNullException>(() => env.CopyToStream(null));
+        // Null FileStream - intentionally passing null to verify exception behavior
+        Should.Throw<ArgumentNullException>(() => env.CopyToStream(null!));
     }
 
     public void stream_throws_exception_for_read_only_file_stream()

src/LightningDB.Tests/LightningDB.Tests.csproj

@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks>net8.0;net9.0;net10.0</TargetFrameworks>
     <LangVersion>13</LangVersion>
+    <Nullable>enable</Nullable>
     <AssemblyName>LightningDB.Tests</AssemblyName>
     <PackageId>LightningDB.Tests</PackageId>
     <GenerateRuntimeConfigurationFiles>true</GenerateRuntimeConfigurationFiles>

src/LightningDB.Tests/TestBase.cs

@@ -13,8 +13,8 @@ protected string TempPath(string seed = "")
       Directory.CreateDirectory(path);
       return path;
    }
-   protected LightningEnvironment CreateEnvironment(string path = null, EnvironmentConfiguration config = null) => 
-      new(path ?? TempPath(), config);
+   protected LightningEnvironment CreateEnvironment(string? path = null, EnvironmentConfiguration? config = null) =>
+      config is null ? new(path ?? TempPath()) : new(path ?? TempPath(), config);
 
    public static void CleanupSession()
    {

src/LightningDB.Tests/TestHelperExtensions.cs

@@ -31,11 +31,11 @@ public static bool ContainsKey(this LightningTransaction tx, LightningDatabase d
         return tx.ContainsKey(db, enc.GetBytes(key));
     }
 
-    public static bool TryGet(this LightningTransaction tx, LightningDatabase db, string key, out string value)
+    public static bool TryGet(this LightningTransaction tx, LightningDatabase db, string key, out string? value)
     {
         var enc = System.Text.Encoding.UTF8;
         var found = tx.TryGet(db, enc.GetBytes(key), out var result);
-        value = enc.GetString(result);
+        value = result is not null ? enc.GetString(result) : null;
         return found;
     }
 
@@ -52,7 +52,7 @@ public static void RunCursorScenario(this LightningEnvironment env,
         DatabaseOpenFlags flags = DatabaseOpenFlags.Create, TransactionBeginFlags transactionFlags = TransactionBeginFlags.None)
     {
         using var tx = env.BeginTransaction(transactionFlags);
-        using var db = tx.OpenDatabase(configuration: new DatabaseConfiguration { Flags = flags });
+        using var db = tx.OpenDatabase(new DatabaseConfiguration { Flags = flags });
         using var cursor = tx.CreateCursor(db);
         scenario(tx, db, cursor);
     }
@@ -62,7 +62,7 @@ public static void RunTransactionScenario(this LightningEnvironment env,
         DatabaseOpenFlags flags = DatabaseOpenFlags.Create, TransactionBeginFlags transactionFlags = TransactionBeginFlags.None)
     {
         using var tx = env.BeginTransaction(transactionFlags);
-        using var db = tx.OpenDatabase(configuration: new DatabaseConfiguration { Flags = flags });
+        using var db = tx.OpenDatabase(new DatabaseConfiguration { Flags = flags });
         scenario(tx, db);
     }
 }

src/LightningDB/DatabaseConfiguration.cs

@@ -12,8 +12,8 @@ namespace LightningDB;
 /// </summary>
 public class DatabaseConfiguration
 {
-    private IComparer<MDBValue> _comparer;
-    private IComparer<MDBValue> _duplicatesComparer;
+    private IComparer<MDBValue>? _comparer;
+    private IComparer<MDBValue>? _duplicatesComparer;
 
     public DatabaseConfiguration()
     {
@@ -51,12 +51,12 @@ internal IDisposable ConfigureDatabase(LightningTransaction tx, LightningDatabas
 
     private int Compare(ref MDBValue left, ref MDBValue right)
     {
-        return _comparer.Compare(left, right);
+        return _comparer!.Compare(left, right);
     }
 
     private int IsDuplicate(ref MDBValue left, ref MDBValue right)
     {
-        return _duplicatesComparer.Compare(left, right);
+        return _duplicatesComparer!.Compare(left, right);
     }
 
     /// <summary>

src/LightningDB/LightningDB.csproj

@@ -6,6 +6,7 @@
     <Authors>Ilya Lukyanov;Corey Kaylor</Authors>
     <TargetFrameworks>netstandard2.0;net8.0;net9.0;net10.0</TargetFrameworks>
     <LangVersion>14</LangVersion>
+    <Nullable>enable</Nullable>
     <AssemblyName>LightningDB</AssemblyName>
     <PackageId>LightningDB</PackageId>
     <PackageIcon>lightningdb.png</PackageIcon>
@@ -34,5 +35,6 @@
 
   <ItemGroup>
     <PackageReference Include="System.Memory" Version="4.6.0" Condition="'$(TargetFramework)' == 'netstandard2.0'" />
+    <PackageReference Include="PolySharp" Version="1.14.1" PrivateAssets="all" Condition="'$(TargetFramework)' == 'netstandard2.0'" />
   </ItemGroup>
 </Project>

src/LightningDB/LightningDatabase.cs

@@ -24,7 +24,7 @@ public sealed class LightningDatabase : IDisposable
     /// <param name="transaction">Active transaction.</param>
     /// <param name="configuration">Options for the database, like encoding, option flags, and comparison logic.</param>
     /// <param name="closeOnDispose">Close database handle on dispose</param>
-    internal LightningDatabase(string name, LightningTransaction transaction, DatabaseConfiguration configuration,
+    internal LightningDatabase(string? name, LightningTransaction transaction, DatabaseConfiguration configuration,
         bool closeOnDispose)
     {
         if (transaction == null)
@@ -55,7 +55,7 @@ internal LightningDatabase(string name, LightningTransaction transaction, Databa
     /// <summary>
     /// Database name.
     /// </summary>
-    public string Name { get; }
+    public string? Name { get; }
 
     /// <summary>
     /// Environment in which the database was opened.

src/LightningDB/LightningEnvironment.cs

@@ -16,24 +16,38 @@ public sealed class LightningEnvironment : IDisposable
 
     internal nint _handle;
 
+    /// <summary>
+    /// Creates a new instance of LightningEnvironment with default configuration.
+    /// </summary>
+    /// <param name="path">Directory for storing database files.</param>
+    public LightningEnvironment(string path)
+    {
+        if (string.IsNullOrWhiteSpace(path))
+            throw new ArgumentException("Invalid directory name");
+
+        mdb_env_create(out _handle).ThrowOnError();
+        _config.Configure(this);
+
+        Path = path;
+    }
+
     /// <summary>
     /// Creates a new instance of LightningEnvironment.
     /// </summary>
     /// <param name="path">Directory for storing database files.</param>
     /// <param name="configuration">Configuration for the environment.</param>
-    public LightningEnvironment(string path, EnvironmentConfiguration configuration = null)
+    public LightningEnvironment(string path, EnvironmentConfiguration configuration)
     {
         if (string.IsNullOrWhiteSpace(path))
             throw new ArgumentException("Invalid directory name");
-
-        var config = configuration ?? _config;
+        if (configuration == null)
+            throw new ArgumentNullException(nameof(configuration));
 
         mdb_env_create(out _handle).ThrowOnError();
-        config.Configure(this);
-        _config = config;
+        configuration.Configure(this);
+        _config = configuration;
 
         Path = path;
-
     }
 
     /// <summary>
@@ -218,47 +232,52 @@ public void Open(EnvironmentOpenFlags openFlags = EnvironmentOpenFlags.None, Uni
     }
 
     /// <summary>
-    /// Create a transaction for use with the environment.
+    /// Create a top-level transaction for use with the environment.
     /// The transaction handle may be discarded using Abort() or Commit().
     /// Note:
     /// Transactions may not span threads; a transaction must only be used by a single thread. Also, a thread may only have a single transaction.
     /// Cursors may not span transactions; each cursor must be opened and closed within a single transaction.
     /// </summary>
-    /// <param name="parent">
-    /// If this parameter is non-NULL, the new transaction will be a nested transaction, with the transaction indicated by parent as its parent.
-    /// Transactions may be nested to any level.
-    /// A parent transaction may not issue any other operations besides BeginTransaction, Abort, or Commit while it has active child transactions.
-    /// </param>
     /// <param name="beginFlags">
     /// Special options for this transaction.
     /// </param>
     /// <returns>
     /// New LightningTransaction
     /// </returns>
-    public LightningTransaction BeginTransaction(LightningTransaction parent = null, TransactionBeginFlags beginFlags = LightningTransaction.DefaultTransactionBeginFlags)
+    public LightningTransaction BeginTransaction(TransactionBeginFlags beginFlags = LightningTransaction.DefaultTransactionBeginFlags)
     {
-        if (!IsOpened)
-            throw new InvalidOperationException("Environment must be opened before starting a transaction");
-
-        return new LightningTransaction(this, parent, beginFlags);
+        return BeginTransactionImpl(null, beginFlags);
     }
 
     /// <summary>
-    /// Create a transaction for use with the environment.
-    /// The transaction handle may be discarded usingAbort() or Commit().
+    /// Create a nested transaction for use with the environment.
+    /// The transaction handle may be discarded using Abort() or Commit().
     /// Note:
     /// Transactions may not span threads; a transaction must only be used by a single thread. Also, a thread may only have a single transaction.
     /// Cursors may not span transactions; each cursor must be opened and closed within a single transaction.
     /// </summary>
+    /// <param name="parent">
+    /// The parent transaction. The new transaction will be a nested transaction.
+    /// Transactions may be nested to any level.
+    /// A parent transaction may not issue any other operations besides BeginTransaction, Abort, or Commit while it has active child transactions.
+    /// </param>
     /// <param name="beginFlags">
     /// Special options for this transaction.
     /// </param>
     /// <returns>
     /// New LightningTransaction
     /// </returns>
-    public LightningTransaction BeginTransaction(TransactionBeginFlags beginFlags)
+    public LightningTransaction BeginTransaction(LightningTransaction parent, TransactionBeginFlags beginFlags = LightningTransaction.DefaultTransactionBeginFlags)
+    {
+        return BeginTransactionImpl(parent, beginFlags);
+    }
+
+    private LightningTransaction BeginTransactionImpl(LightningTransaction? parent, TransactionBeginFlags beginFlags)
     {
-        return BeginTransaction(null, beginFlags);
+        if (!IsOpened)
+            throw new InvalidOperationException("Environment must be opened before starting a transaction");
+
+        return new LightningTransaction(this, parent, beginFlags);
     }
 
     /// <summary>

src/LightningDB/LightningExtensions.cs

@@ -52,7 +52,7 @@ public static (MDBResultCode resultCode, MDBValue key, MDBValue value) ThrowOnRe
     private static string mdb_strerror(int err)
     {
         var ptr = Lmdb.mdb_strerror(err);
-        return Marshal.PtrToStringAnsi(ptr);
+        return Marshal.PtrToStringAnsi(ptr) ?? $"Unknown error {err}";
     }
 
     /// <summary>
@@ -124,11 +124,11 @@ private static IEnumerable<MDBValue> AllValuesForImpl(this LightningCursor curso
     /// <param name="value">A byte array containing the value found in the database, if it exists.</param>
     /// <returns>True if key exists, false if not.</returns>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static bool TryGet(this LightningTransaction tx, LightningDatabase db, byte[] key, out byte[] value)
+    public static bool TryGet(this LightningTransaction tx, LightningDatabase db, byte[] key, out byte[]? value)
     {
         return TryGet(tx, db, key.AsSpan(), out value);
     }
-        
+
     /// <summary>
     /// Tries to get a value by its key.
     /// </summary>
@@ -138,7 +138,7 @@ public static bool TryGet(this LightningTransaction tx, LightningDatabase db, by
     /// <param name="value">A byte array containing the value found in the database, if it exists.</param>
     /// <returns>True if key exists, false if not.</returns>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static bool TryGet(this LightningTransaction tx, LightningDatabase db, ReadOnlySpan<byte> key, out byte[] value)
+    public static bool TryGet(this LightningTransaction tx, LightningDatabase db, ReadOnlySpan<byte> key, out byte[]? value)
     {
         var (resultCode, _, mdbValue) = tx.Get(db, key);
         if (resultCode == MDBResultCode.Success)