handling of blank paths during validation.

NzbDrone.Api/Validation/PathValidator.cs

@@ -12,6 +12,7 @@ namespace NzbDrone.Api.Validation
 
         protected override bool IsValid(PropertyValidatorContext context)
         {
+            if (context.PropertyValue == null) return false;
             return context.PropertyValue.ToString().IsPathValid();
         }
     }

NzbDrone.Common/PathExtensions.cs

@@ -50,7 +50,7 @@ namespace NzbDrone.Common
 
         public static bool IsPathValid(this string path)
         {
-            if (path.ContainsInvalidPathChars())
+            if (path.ContainsInvalidPathChars() || string.IsNullOrWhiteSpace(path))
             {
                 return false;
             }