diff --git a/src/SMAPI.Internal.Patching/BasePatcher.cs b/src/SMAPI.Internal.Patching/BasePatcher.cs
index 6d019b52..c1936ccc 100644
--- a/src/SMAPI.Internal.Patching/BasePatcher.cs
+++ b/src/SMAPI.Internal.Patching/BasePatcher.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Reflection;
 using HarmonyLib;
@@ -32,7 +30,7 @@ namespace StardewModdingAPI.Internal.Patching
         /// <param name="name">The method name.</param>
         /// <param name="parameters">The method parameter types, or <c>null</c> if it's not overloaded.</param>
         /// <param name="generics">The method generic types, or <c>null</c> if it's not generic.</param>
-        protected MethodInfo RequireMethod<TTarget>(string name, Type[] parameters = null, Type[] generics = null)
+        protected MethodInfo RequireMethod<TTarget>(string name, Type[]? parameters = null, Type[]? generics = null)
         {
             return PatchHelper.RequireMethod<TTarget>(name, parameters, generics);
         }
@@ -42,7 +40,7 @@ namespace StardewModdingAPI.Internal.Patching
         /// <param name="priority">The patch priority to apply, usually specified using Harmony's <see cref="Priority"/> enum, or <c>null</c> to keep the default value.</param>
         protected HarmonyMethod GetHarmonyMethod(string name, int? priority = null)
         {
-            var method = new HarmonyMethod(
+            HarmonyMethod method = new(
                 AccessTools.Method(this.GetType(), name)
                 ?? throw new InvalidOperationException($"Can't find patcher method {PatchHelper.GetMethodString(this.GetType(), name)}.")
             );
diff --git a/src/SMAPI.Internal.Patching/HarmonyPatcher.cs b/src/SMAPI.Internal.Patching/HarmonyPatcher.cs
index fc239fd2..6f30c241 100644
--- a/src/SMAPI.Internal.Patching/HarmonyPatcher.cs
+++ b/src/SMAPI.Internal.Patching/HarmonyPatcher.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using HarmonyLib;
 
diff --git a/src/SMAPI.Internal.Patching/IPatcher.cs b/src/SMAPI.Internal.Patching/IPatcher.cs
index 5b373117..a732d64f 100644
--- a/src/SMAPI.Internal.Patching/IPatcher.cs
+++ b/src/SMAPI.Internal.Patching/IPatcher.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using HarmonyLib;
 
 namespace StardewModdingAPI.Internal.Patching
diff --git a/src/SMAPI.Internal.Patching/PatchHelper.cs b/src/SMAPI.Internal.Patching/PatchHelper.cs
index 52b15fd1..edd8ef57 100644
--- a/src/SMAPI.Internal.Patching/PatchHelper.cs
+++ b/src/SMAPI.Internal.Patching/PatchHelper.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Linq;
 using System.Reflection;
@@ -18,7 +16,7 @@ namespace StardewModdingAPI.Internal.Patching
         /// <typeparam name="TTarget">The type containing the method.</typeparam>
         /// <param name="parameters">The method parameter types, or <c>null</c> if it's not overloaded.</param>
         /// <exception cref="InvalidOperationException">The type has no matching constructor.</exception>
-        public static ConstructorInfo RequireConstructor<TTarget>(Type[] parameters = null)
+        public static ConstructorInfo RequireConstructor<TTarget>(Type[]? parameters = null)
         {
             return
                 AccessTools.Constructor(typeof(TTarget), parameters)
@@ -31,7 +29,7 @@ namespace StardewModdingAPI.Internal.Patching
         /// <param name="parameters">The method parameter types, or <c>null</c> if it's not overloaded.</param>
         /// <param name="generics">The method generic types, or <c>null</c> if it's not generic.</param>
         /// <exception cref="InvalidOperationException">The type has no matching method.</exception>
-        public static MethodInfo RequireMethod<TTarget>(string name, Type[] parameters = null, Type[] generics = null)
+        public static MethodInfo RequireMethod<TTarget>(string name, Type[]? parameters = null, Type[]? generics = null)
         {
             return
                 AccessTools.Method(typeof(TTarget), name, parameters, generics)
@@ -43,7 +41,7 @@ namespace StardewModdingAPI.Internal.Patching
         /// <param name="name">The method name, or <c>null</c> for a constructor.</param>
         /// <param name="parameters">The method parameter types, or <c>null</c> if it's not overloaded.</param>
         /// <param name="generics">The method generic types, or <c>null</c> if it's not generic.</param>
-        public static string GetMethodString(Type type, string name, Type[] parameters = null, Type[] generics = null)
+        public static string GetMethodString(Type type, string? name, Type[]? parameters = null, Type[]? generics = null)
         {
             StringBuilder str = new();
 
diff --git a/src/SMAPI.Internal/ConsoleWriting/ColorSchemeConfig.cs b/src/SMAPI.Internal/ConsoleWriting/ColorSchemeConfig.cs
index b22aa231..4e5850ea 100644
--- a/src/SMAPI.Internal/ConsoleWriting/ColorSchemeConfig.cs
+++ b/src/SMAPI.Internal/ConsoleWriting/ColorSchemeConfig.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 
@@ -8,10 +6,26 @@ namespace StardewModdingAPI.Internal.ConsoleWriting
     /// <summary>The console color scheme options.</summary>
     internal class ColorSchemeConfig
     {
+        /*********
+        ** Accessors
+        *********/
         /// <summary>The default color scheme ID to use, or <see cref="MonitorColorScheme.AutoDetect"/> to select one automatically.</summary>
-        public MonitorColorScheme UseScheme { get; set; }
+        public MonitorColorScheme UseScheme { get; }
 
         /// <summary>The available console color schemes.</summary>
-        public IDictionary<MonitorColorScheme, IDictionary<ConsoleLogLevel, ConsoleColor>> Schemes { get; set; }
+        public IDictionary<MonitorColorScheme, IDictionary<ConsoleLogLevel, ConsoleColor>> Schemes { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="useScheme">The default color scheme ID to use, or <see cref="MonitorColorScheme.AutoDetect"/> to select one automatically.</param>
+        /// <param name="schemes">The available console color schemes.</param>
+        public ColorSchemeConfig(MonitorColorScheme useScheme, IDictionary<MonitorColorScheme, IDictionary<ConsoleLogLevel, ConsoleColor>> schemes)
+        {
+            this.UseScheme = useScheme;
+            this.Schemes = schemes;
+        }
     }
 }
diff --git a/src/SMAPI.Internal/ConsoleWriting/ColorfulConsoleWriter.cs b/src/SMAPI.Internal/ConsoleWriting/ColorfulConsoleWriter.cs
index 19a31c7b..78db0d65 100644
--- a/src/SMAPI.Internal/ConsoleWriting/ColorfulConsoleWriter.cs
+++ b/src/SMAPI.Internal/ConsoleWriting/ColorfulConsoleWriter.cs
@@ -1,7 +1,6 @@
-#nullable disable
-
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using StardewModdingAPI.Toolkit.Utilities;
 
 namespace StardewModdingAPI.Internal.ConsoleWriting
@@ -13,10 +12,11 @@ namespace StardewModdingAPI.Internal.ConsoleWriting
         ** Fields
         *********/
         /// <summary>The console text color for each log level.</summary>
-        private readonly IDictionary<ConsoleLogLevel, ConsoleColor> Colors;
+        private readonly IDictionary<ConsoleLogLevel, ConsoleColor>? Colors;
 
         /// <summary>Whether the current console supports color formatting.</summary>
-        private readonly bool SupportsColor;
+        [MemberNotNullWhen(true, nameof(ColorfulConsoleWriter.Colors))]
+        private bool SupportsColor { get; }
 
 
         /*********
@@ -74,10 +74,9 @@ namespace StardewModdingAPI.Internal.ConsoleWriting
         /// <remarks>The colors here should be kept in sync with the SMAPI config file.</remarks>
         public static ColorSchemeConfig GetDefaultColorSchemeConfig(MonitorColorScheme useScheme)
         {
-            return new ColorSchemeConfig
-            {
-                UseScheme = useScheme,
-                Schemes = new Dictionary<MonitorColorScheme, IDictionary<ConsoleLogLevel, ConsoleColor>>
+            return new ColorSchemeConfig(
+                useScheme: useScheme,
+                schemes: new Dictionary<MonitorColorScheme, IDictionary<ConsoleLogLevel, ConsoleColor>>
                 {
                     [MonitorColorScheme.DarkBackground] = new Dictionary<ConsoleLogLevel, ConsoleColor>
                     {
@@ -100,7 +99,7 @@ namespace StardewModdingAPI.Internal.ConsoleWriting
                         [ConsoleLogLevel.Success] = ConsoleColor.DarkGreen
                     }
                 }
-            };
+            );
         }
 
 
@@ -136,7 +135,7 @@ namespace StardewModdingAPI.Internal.ConsoleWriting
             }
 
             // get colors for scheme
-            return colorConfig.Schemes.TryGetValue(schemeID, out IDictionary<ConsoleLogLevel, ConsoleColor> scheme)
+            return colorConfig.Schemes.TryGetValue(schemeID, out IDictionary<ConsoleLogLevel, ConsoleColor>? scheme)
                 ? scheme
                 : throw new NotSupportedException($"Unknown color scheme '{schemeID}'.");
         }
diff --git a/src/SMAPI.Internal/ConsoleWriting/IConsoleWriter.cs b/src/SMAPI.Internal/ConsoleWriting/IConsoleWriter.cs
index 84e17207..fbcf161c 100644
--- a/src/SMAPI.Internal/ConsoleWriting/IConsoleWriter.cs
+++ b/src/SMAPI.Internal/ConsoleWriting/IConsoleWriter.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 namespace StardewModdingAPI.Internal.ConsoleWriting
 {
     /// <summary>Writes text to the console.</summary>
diff --git a/src/SMAPI.Internal/ExceptionHelper.cs b/src/SMAPI.Internal/ExceptionHelper.cs
index a856cf71..7edc0f62 100644
--- a/src/SMAPI.Internal/ExceptionHelper.cs
+++ b/src/SMAPI.Internal/ExceptionHelper.cs
@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.Reflection;
 using System.Text.RegularExpressions;
@@ -14,7 +12,7 @@ namespace StardewModdingAPI.Internal
         *********/
         /// <summary>Get a string representation of an exception suitable for writing to the error log.</summary>
         /// <param name="exception">The error to summarize.</param>
-        public static string GetLogSummary(this Exception exception)
+        public static string GetLogSummary(this Exception? exception)
         {
             try
             {
@@ -27,7 +25,7 @@ namespace StardewModdingAPI.Internal
 
                     case ReflectionTypeLoadException ex:
                         string summary = ex.ToString();
-                        foreach (Exception childEx in ex.LoaderExceptions)
+                        foreach (Exception? childEx in ex.LoaderExceptions)
                             summary += $"\n\n{childEx?.GetLogSummary()}";
                         message = summary;
                         break;