resolve package name from folder name

src/Umbraco.Core/Manifest/PackageManifest.cs

@@ -1,6 +1,8 @@
 using System;
+using System.IO;
 using System.Runtime.Serialization;
 using Umbraco.Cms.Core.PropertyEditors;
+using Umbraco.Extensions;
 
 namespace Umbraco.Cms.Core.Manifest
 {
@@ -10,10 +12,30 @@ namespace Umbraco.Cms.Core.Manifest
     [DataContract]
     public class PackageManifest
     {
-        [DataMember(Name = "name", IsRequired = false)]
-        public string PackageName { get; set; }
+        private string _packageName;
 
-        [DataMember(Name = "packageView", IsRequired = false)]
+        /// <summary>
+        /// An optional package name. If not specified then the directory name is used.
+        /// </summary>
+        [DataMember(Name = "name")]
+        public string PackageName
+        {
+            get
+            {
+                if (!_packageName.IsNullOrWhiteSpace())
+                {
+                    return _packageName;
+                }
+                if (!Source.IsNullOrWhiteSpace())
+                {
+                    _packageName = Path.GetFileName(Path.GetDirectoryName(Source));
+                }
+                return _packageName;
+            }
+            set => _packageName = value;
+        }
+
+        [DataMember(Name = "packageView")]
         public string PackageView { get; set; }
 
         /// <summary>

src/Umbraco.Infrastructure/Manifest/ManifestParser.cs

@@ -170,7 +170,10 @@ namespace Umbraco.Cms.Core.Manifest
         private IEnumerable<string> GetManifestFiles()
         {
             if (Directory.Exists(_path) == false)
-                return new string[0];
+            {
+                return Array.Empty<string>();
+            }
+
             return Directory.GetFiles(_path, "package.manifest", SearchOption.AllDirectories);
         }