fix int overflow in FTI model convertor (#2053)

* fix int overflow in fti model convertor

* fix if feature_types are not defined

* fix for absence of feature_type attribute

---------

Co-authored-by: Dmitry Razdoburdin <>

src/gbt_convertors.pyx

@@ -253,6 +253,17 @@ class TreeList(list):
         Note: We cannot type-hint the xgb.Booster without loading xgb as dependency in pyx code,
               therefore not type hint is added.
         """
+        # dump_format="json" is affected by the integer-overflow error,
+        # since XGBoost doesn't control numeric limits of integer features.
+        # For correct conversion we manulally replace feature types from 'int'->'float;
+        if hasattr(booster, "feature_types"):
+            feature_types = booster.feature_types
+            if feature_types:
+                for i in range(len(feature_types)):
+                    if feature_types[i] == "int":
+                        feature_types[i] = "float"
+                booster.feature_types = feature_types
+
         tl = TreeList()
         dump = booster.get_dump(dump_format="json", with_stats=True)
         for tree_id, raw_tree in enumerate(dump):