Fix #1907: Discard parameter names containing non-printable or white space characters from set of possible names considered by AssignVariableNames.

ICSharpCode.Decompiler/CSharp/OutputVisitor/TextWriterTokenWriter.cs

@@ -477,6 +477,21 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			return sb.ToString();
 		}
 
+		public static bool ContainsNonPrintableIdentifierChar(string identifier)
+		{
+			if (string.IsNullOrEmpty(identifier))
+				return false;
+
+			for (int i = 0; i < identifier.Length; i++) {
+				if (char.IsWhiteSpace(identifier[i]))
+					return true;
+				if (!IsPrintableIdentifierChar(identifier, i))
+					return true;
+			}
+
+			return false;
+		}
+
 		static bool IsPrintableIdentifierChar(string identifier, int index)
 		{
 			switch (identifier[index]) {

ICSharpCode.Decompiler/IL/Transforms/AssignVariableNames.cs

@@ -23,6 +23,7 @@ using System.Reflection;
 using System.Text;
 using System.Threading.Tasks;
 using Humanizer;
+using ICSharpCode.Decompiler.CSharp.OutputVisitor;
 using ICSharpCode.Decompiler.IL;
 using ICSharpCode.Decompiler.Semantics;
 using ICSharpCode.Decompiler.TypeSystem;
@@ -421,7 +422,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				// remove the 'I' for interfaces
 				if (name.Length >= 3 && name[0] == 'I' && char.IsUpper(name[1]) && char.IsLower(name[2]))
 					name = name.Substring(1);
-				name = CleanUpVariableName(name);
+				name = CleanUpVariableName(name) ?? "obj";
 			}
 			return name;
 		}
@@ -466,6 +467,10 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 			else if (name.Length > 1 && name[0] == '_' && (char.IsLetter(name[1]) || name[1] == '_'))
 				name = name.Substring(1);
 
+			if (TextWriterTokenWriter.ContainsNonPrintableIdentifierChar(name)) {
+				return null;
+			}
+
 			if (name.Length == 0)
 				return "obj";
 			else