Fix warnings from nullabilty

PortableExecutable/Executable.cs

@@ -12,24 +12,40 @@ namespace SabreTools.Models.PortableExecutable
         /// <summary>
         /// MS-DOS executable stub
         /// </summary>
+#if NET48
         public MSDOS.Executable Stub { get; set; }
+#else
+        public MSDOS.Executable? Stub { get; set; }
+#endif
 
         /// <summary>
         /// After the MS-DOS stub, at the file offset specified at offset 0x3c, is a 4-byte
         /// signature that identifies the file as a PE format image file. This signature is "PE\0\0"
         /// (the letters "P" and "E" followed by two null bytes).
         /// </summary>
+#if NET48
         public string Signature { get; set; }
+#else
+        public string? Signature { get; set; }
+#endif
 
         /// <summary>
         /// COFF file header
         /// </summary>
+#if NET48
         public COFFFileHeader COFFFileHeader { get; set; }
+#else
+        public COFFFileHeader? COFFFileHeader { get; set; }
+#endif
 
         /// <summary>
         /// Optional header
         /// </summary>
+#if NET48
         public OptionalHeader OptionalHeader { get; set; }
+#else
+        public OptionalHeader? OptionalHeader { get; set; }
+#endif
 
         // TODO: Support grouped sections in section reading and parsing
         // https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#grouped-sections-object-only
@@ -40,27 +56,47 @@ namespace SabreTools.Models.PortableExecutable
         /// <summary>
         /// Section table
         /// </summary>
+#if NET48
         public SectionHeader[] SectionTable { get; set; }
+#else
+        public SectionHeader[]? SectionTable { get; set; }
+#endif
 
         /// <summary>
         /// COFF symbol table
         /// </summary>
+#if NET48
         public COFFSymbolTableEntry[] COFFSymbolTable { get; set; }
+#else
+        public COFFSymbolTableEntry[]? COFFSymbolTable { get; set; }
+#endif
 
         /// <summary>
         /// COFF string table
         /// </summary>
+#if NET48
         public COFFStringTable COFFStringTable { get; set; }
+#else
+        public COFFStringTable? COFFStringTable { get; set; }
+#endif
 
         /// <summary>
         /// Attribute certificate table
         /// </summary>
+#if NET48
         public AttributeCertificateTableEntry[] AttributeCertificateTable { get; set; }
+#else
+        public AttributeCertificateTableEntry[]? AttributeCertificateTable { get; set; }
+#endif
 
         /// <summary>
         /// Delay-load directory table
         /// </summary>
+#if NET48
         public DelayLoadDirectoryTable DelayLoadDirectoryTable { get; set; }
+#else
+        public DelayLoadDirectoryTable? DelayLoadDirectoryTable { get; set; }
+#endif
 
         #region Named Sections
 
@@ -71,12 +107,20 @@ namespace SabreTools.Models.PortableExecutable
         /// <summary>
         /// Base relocation table (.reloc)
         /// </summary>
+#if NET48
         public BaseRelocationBlock[] BaseRelocationTable { get; set; }
+#else
+        public BaseRelocationBlock[]? BaseRelocationTable { get; set; }
+#endif
 
         /// <summary>
         /// Debug table (.debug*)
         /// </summary>
+#if NET48
         public DebugTable DebugTable { get; set; }
+#else
+        public DebugTable? DebugTable { get; set; }
+#endif
 
         // .drectve - A section is a directive section if it has the IMAGE_SCN_LNK_INFO
         // flag set in the section header and has the .drectve section name. The linker
@@ -97,17 +141,29 @@ namespace SabreTools.Models.PortableExecutable
         /// <summary>
         /// Export table (.edata)
         /// </summary>
+#if NET48
         public ExportTable ExportTable { get; set; }
+#else
+        public ExportTable? ExportTable { get; set; }
+#endif
 
         /// <summary>
         /// Import table (.idata)
         /// </summary>
+#if NET48
         public ImportTable ImportTable { get; set; }
+#else
+        public ImportTable? ImportTable { get; set; }
+#endif
 
         /// <summary>
         /// Resource directory table (.rsrc)
         /// </summary>
+#if NET48
         public ResourceDirectoryTable ResourceDirectoryTable { get; set; }
+#else
+        public ResourceDirectoryTable? ResourceDirectoryTable { get; set; }
+#endif
 
         // .sxdata - The valid exception handlers of an object are listed in the .sxdata
         // section of that object. The section is marked IMAGE_SCN_LNK_INFO. It contains