message: [pdsl_core] storage::HashMap::len() now defaults to 0
  Before this change it was relying on an initialized storage value.
diff: @@ -88,10 +88,7 @@ impl<K, V> HashMap<K, V> {
  *self
  .len
  .get()
  - .expect(
  - "[pdsl_core::HashMap] Error: \
  - expected a value at storage slot associated with the len field"
  - )
  + .unwrap_or(&0)
  }
  /// Returns `true` if the map contains no elements.
  