BUG: correct encoding for trapezoidal sweep length and angle.

Author: phmbressan

rocketpy/rocket/aero_surface/fins/trapezoidal_fins.py

@@ -3,6 +3,7 @@
 from rocketpy.plots.aero_surface_plots import _TrapezoidalFinsPlots
 from rocketpy.prints.aero_surface_prints import _TrapezoidalFinsPrints
 
+from typing import Iterable
 from .fins import Fins
 
 
@@ -351,12 +352,12 @@ def all_info(self):
     def to_dict(self, **kwargs):
         data = super().to_dict(**kwargs)
         data["tip_chord"] = self.tip_chord
-
+        data["sweep_length"] = self.sweep_length,
+        data["sweep_angle"] = self.sweep_angle,
+        
         if kwargs.get("include_outputs", False):
             data.update(
                 {
-                    "sweep_length": self.sweep_length,
-                    "sweep_angle": self.sweep_angle,
                     "shape_vec": self.shape_vec,
                     "Af": self.Af,
                     "AR": self.AR,
@@ -373,6 +374,19 @@ def to_dict(self, **kwargs):
 
     @classmethod
     def from_dict(cls, data):
+        sweep_angle = None
+        sweep_length = None
+        
+        if data.get("sweep_angle") is None and data.get("sweep_length") is not None:
+            sweep_length = data.get("sweep_length")
+            if isinstance(sweep_length, Iterable) and sweep_length:
+                sweep_length = sweep_length[0]
+                
+        if sweep_length is None and data.get("sweep_angle") is not None:
+            sweep_angle = data.get("sweep_angle")
+            if isinstance(sweep_angle, Iterable) and sweep_angle:
+                sweep_angle = sweep_angle[0]
+        
         return cls(
             n=data["n"],
             root_chord=data["root_chord"],
@@ -382,4 +396,6 @@ def from_dict(cls, data):
             cant_angle=data["cant_angle"],
             airfoil=data["airfoil"],
             name=data["name"],
+            sweep_length=sweep_length,
+            sweep_angle=sweep_angle,
         )