Misc. cleanup

src/Interactive/Features/Interactive/Core/NuGetPackageResolverImpl.cs

@@ -87,7 +87,7 @@ internal override ImmutableArray<string> ResolveNuGetPackage(string packageName,
             catch (UnauthorizedAccessException)
             {
             }
-            return default(ImmutableArray<string>);
+            return ImmutableArray<string>.Empty;
         }
 
         /// <summary>

src/Interactive/HostTest/NuGetPackageResolverTests.cs

@@ -126,7 +126,7 @@ public void HandledException()
                 bool restored = false;
                 var resolver = new NuGetPackageResolverImpl(directory.Path, startInfo => { restored = true; throw new IOException(); });
                 var actualPaths = resolver.ResolveNuGetPackage("A.B.C", "1.2");
-                Assert.True(actualPaths.IsDefault);
+                Assert.True(actualPaths.IsEmpty);
                 Assert.True(restored);
             }
         }

src/Scripting/Core/Resolvers/RuntimeMetadataReferenceResolver.cs

@@ -25,9 +25,7 @@ internal sealed class RuntimeMetadataReferenceResolver : MetadataReferenceResolv
         internal RuntimeMetadataReferenceResolver(
             ImmutableArray<string> searchPaths,
             string baseDirectory)
-            : this(new RelativePathResolver(searchPaths.NullToEmpty(), baseDirectory),
-                   null,
-                   GacFileResolver.Default)
+            : this(new RelativePathResolver(searchPaths, baseDirectory), null, GacFileResolver.Default)
         {
         }