Implicit conversion from FileInfo to FileInfoBase (#348)

* Implicit conversion from FileInfo to FileInfoBase

* Added unit test for conversion of null FileInfo to FileInfoBase.

Fixes #348

Author: m-ringler

System.IO.Abstractions.TestingHelpers.Tests/FileInfoBaseConversionTests.cs

@@ -0,0 +1,26 @@
+namespace System.IO.Abstractions.TestingHelpers.Tests
+{
+    using NUnit.Framework;
+
+    /// <summary>
+    /// Unit tests for the conversion operators of the <see cref="FileInfoBase"/> class.
+    /// </summary>
+    public class FileInfoBaseConversionTests
+    {
+        /// <summary>
+        /// Tests that a <c>null</c> <see cref="FileInfo"/> is correctly converted to a <c>null</c> <see cref="FileInfoBase"/> without exception.
+        /// </summary>
+        [Test]
+        public void FileInfoBase_FromFileInfo_ShouldReturnNullIfFileInfoIsNull()
+        {
+            // Arrange
+            FileInfo fileInfo = null;
+
+            // Act
+            FileInfoBase actual = fileInfo;
+
+            // Assert
+            Assert.IsNull(actual);
+        }
+    }
+}

System.IO.Abstractions/FileInfoBase.cs

@@ -81,7 +81,12 @@ public abstract class FileInfoBase : FileSystemInfoBase
 
         public static implicit operator FileInfoBase(FileInfo fileInfo)
         {
+            if (fileInfo == null)
+            {
+                return null;
+            }
+            
             return new FileInfoWrapper(fileInfo);
         }
     }
-}
+}