Fix: ignore missing null values when comparing PIEs

Problem: the new implementation of `CairoPie` using the
`CairoPieAdditionalData` struct makes it hard to reproduce the exact
same behaviour as `cairo-lang` when handling builtins with no data.
While `cairo-lang` will generate a null value and include it in the JSON
file, we can only (easily) generate a null value for each builtin or for
none of them.

Solution: make the comparator script more flexible by filtering out null
values from JSON contents.

vm/src/tests/cairo_pie_comparator.py

@@ -2,6 +2,7 @@
 
 import sys
 import json
+from typing import Any
 from zipfile import ZipFile
 import memory_comparator
 
@@ -10,18 +11,36 @@
 
 json_files = ["version.json", "metadata.json", "execution_resources.json", "additional_data.json"]
 
+
+def filter_null_values(content: Any) -> Any:
+    if isinstance(content, dict):
+        return {k: v for k, v in content.items() if v is not None}
+
+    return content
+
+
+def json_contents_are_equivalent(cl: Any, cv: Any) -> bool:
+    """
+    Compares the two JSON contents. and returns whether they are equivalent.
+    Contents are considered equivalent if they are equal or if some keys have null values in one
+    content and are just missing from the other.
+    """
+
+    return filter_null_values(cl) == filter_null_values(cv)
+
+
 with ZipFile(filename1) as cairo_lang_pie_zip, ZipFile(filename2) as cairo_vm_pie_zip:
     # Compare json files
     for file in json_files:
         with cairo_lang_pie_zip.open(file) as cairo_lang_file, cairo_vm_pie_zip.open(file) as cairo_vm_file:
             cl_content = json.load(cairo_lang_file)
             cv_content = json.load(cairo_vm_file)
-            if cl_content != cv_content:
+            if not json_contents_are_equivalent(cl_content, cv_content):
                 print(f"Comparison unsuccesful for {filename1}/{file}  vs {filename2}/{file}")
                 exit(1)
 
     # Compare binary files
-    with cairo_lang_pie_zip.open("memory.bin", 'r') as f1,  cairo_vm_pie_zip.open("memory.bin", 'r') as f2:
+    with cairo_lang_pie_zip.open("memory.bin", 'r') as f1, cairo_vm_pie_zip.open("memory.bin", 'r') as f2:
         memory_comparator.compare_memory_file_contents(f1.read(), f2.read())
 
     print(f"Comparison succesful for {filename1} vs {filename2}")