Update ImageLoader.cs

Author: mstfbl

src/Microsoft.ML.ImageAnalytics/ImageLoader.cs

@@ -88,14 +88,14 @@ internal sealed class Options : TransformInputBase
         /// <param name="env">The host environment.</param>
         /// <param name="imageFolder">Folder where to look for images.</param>
         /// <param name="columns">Names of input and output columns.</param>
-        internal ImageLoadingTransformer(IHostEnvironment env, string imageFolder, params (string outputColumnName, string inputColumnName)[] columns)
+        internal ImageLoadingTransformer(IHostEnvironment env, string imageFolder = null, params (string outputColumnName, string inputColumnName)[] columns)
             : base(Contracts.CheckRef(env, nameof(env)).Register(nameof(ImageLoadingTransformer)), columns)
         {
-            if (String.IsNullOrWhiteSpace(imageFolder) || !File.Exists(imageFolder))
-            {
-                throw new ArgumentException("The provided ImageFolder path {0} is invalid.", imageFolder);
-            }
-            ImageFolder = imageFolder;
+            // Throws ArgumentException if given imageFolder path is invalid or empty. Note: imageFolder may be null in this case.
+            if (imageFolder != null)
+                ImageFolder = Path.GetFullPath(imageFolder);
+            else
+                ImageFolder = null;
             _useImageType = true;
         }
 
@@ -106,11 +106,14 @@ internal ImageLoadingTransformer(IHostEnvironment env, string imageFolder, param
         /// <param name="imageFolder">Folder where to look for images.</param>
         /// <param name="type">Image type flag - true for ImageDataViewType or false for VectorDataViewType. Defaults to true i.e. ImageDataViewType if not specified.</param>
         /// <param name="columns">Names of input and output columns.</param>
-        internal ImageLoadingTransformer(IHostEnvironment env, string imageFolder, bool type = true, params (string outputColumnName, string inputColumnName)[] columns)
+        internal ImageLoadingTransformer(IHostEnvironment env, string imageFolder = null, bool type = true, params (string outputColumnName, string inputColumnName)[] columns)
             : base(Contracts.CheckRef(env, nameof(env)).Register(nameof(ImageLoadingTransformer)), columns)
         {
-            // Throws ArgumentException if given path is invalid/empty, ArgumentNullException if given path is null
-            ImageFolder = Path.GetFullPath(imageFolder);
+            // Throws ArgumentException if given imageFolder path is invalid or empty. Note: imageFolder may be null in this case.
+            if (imageFolder != null)
+                ImageFolder = Path.GetFullPath(imageFolder);
+            else
+                ImageFolder = null;
             _useImageType = type;
         }