ReadList[] handling Null and Hold[] expressions (#1203)

See the `ReadList[]` example in Mathics3/Mathics3-Package-Rubi#2

---------

Co-authored-by: Aravindh Krishnamoorthy <aravindh.krishnamoorthy@fau.de>

Author: rocky

mathics/eval/files_io/files.py

@@ -200,7 +200,9 @@ def eval_Read(
                     except Exception as e:
                         print(e)
 
-                if expr is SymbolEndOfFile:
+                if expr is None:
+                    result.append(None)
+                elif expr is SymbolEndOfFile:
                     evaluation.message(name, "readt", tmp, String(stream.name))
                     return SymbolFailed
                 elif isinstance(expr, BaseElement):
@@ -275,5 +277,10 @@ def eval_Read(
             return [from_python(part) for part in result]
         elif result_len == 1:
             result = result[0]
+            if SymbolHoldExpression in types:
+                if hasattr(result, "head") and result.head is SymbolHold:
+                    return from_python(result)
+                else:
+                    return Expression(SymbolHold, from_python(result))
 
     return from_python(result)

test/builtin/files_io/test_files.py

@@ -295,6 +295,18 @@ def test_close():
             "{{a, 1}}",
             "",
         ),
+        (
+            'ReadList[StringToStream["(**)"], Expression]',
+            None,
+            "{Null}",
+            "",
+        ),
+        (
+            'ReadList[StringToStream["Hold[1+2]"], Expression]',
+            None,
+            "{Hold[1 + 2]}",
+            "",
+        ),
         ('stream = StringToStream["Mathics is cool!"];', None, "Null", ""),
         ("SetStreamPosition[stream, -5]", ("Invalid I/O Seek.",), "0", ""),
         (