Removed check for NullLiteralExpression

src/EditorFeatures/CSharpTest/Diagnostics/RemoveUnnecessaryCast/RemoveUnnecessaryCastTests.cs

@@ -3913,5 +3913,28 @@ static void Main(dynamic p)
     }
 }");
         }
+
+        [WorkItem(18978, "https://github.com/dotnet/roslyn/issues/18978")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsRemoveUnnecessaryCast)]
+        public async Task DontRemoveCastCallToMethodWithParamsArgs()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"
+class Program
+{
+    public static void Main(string[] args)
+    {
+        var takesArgs = new[] { ""Hello"", ""World"" };
+        TakesParams(takesArgs);
+        TakesParams([|(object)takesArgs|]);
+    }
+
+    private static void TakesParams(params object[] foo)
+    {
+        Console.WriteLine(foo.Length);
+    }
+}");
+        }
+        
     }
 }
\ No newline at end of file

src/Workspaces/CSharp/Portable/Extensions/CastExpressionSyntaxExtensions.cs

@@ -161,8 +161,6 @@ private static bool UserDefinedConversionIsAllowed(ExpressionSyntax expression,
             //
             // Foo((object)null);
 
-            if (cast.Expression.WalkDownParentheses().IsKind(SyntaxKind.NullLiteralExpression))
-            {
             var argument = cast.WalkUpParentheses().Parent as ArgumentSyntax;
             if (argument != null)
             {
@@ -200,7 +198,6 @@ private static bool UserDefinedConversionIsAllowed(ExpressionSyntax expression,
                     }
                 }
             }
-            }
 
             return false;
         }