add defaults for the several structs

src/geometry/broad_phase_multi_sap/broad_phase_pair_event.rs

@@ -33,6 +33,12 @@ impl ColliderPair {
     }
 }
 
+impl Default for ColliderPair{
+    fn default() -> Self {
+        ColliderPair::zero()
+    }
+}
+
 /// An event emitted by the broad-phase.
 pub enum BroadPhasePairEvent {
     /// A potential new collision pair has been detected by the broad-phase.

src/geometry/collider_components.rs

@@ -6,7 +6,7 @@ use crate::pipeline::{ActiveEvents, ActiveHooks};
 use std::ops::{Deref, DerefMut};
 
 /// The unique identifier of a collider added to a collider set.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Default)]
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
 #[repr(transparent)]
 pub struct ColliderHandle(pub crate::data::arena::Index);

src/geometry/narrow_phase.rs

@@ -24,7 +24,7 @@ use std::collections::HashMap;
 use std::sync::Arc;
 
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
 struct ColliderGraphIndices {
     contact_graph_index: ColliderGraphIndex,
     intersection_graph_index: ColliderGraphIndex,