Use `zero` instead of `default` for empty values

src/builder.rs

@@ -86,7 +86,7 @@ impl RecipientInfo {
         RecipientInfo {
             ovk: None,
             recipient,
-            value: NoteValue::default(),
+            value: NoteValue::zero(),
             memo: None,
         }
     }
@@ -280,7 +280,7 @@ impl Builder {
         // Determine the value balance for this bundle, ensuring it is valid.
         let value_balance: ValueSum = pre_actions
             .iter()
-            .fold(Ok(ValueSum::default()), |acc, action| {
+            .fold(Ok(ValueSum::zero()), |acc, action| {
                 acc? + action.value_sum()?
             })?;
 

src/value.rs

@@ -80,6 +80,11 @@ impl Sub for NoteValue {
 pub struct ValueSum(i64);
 
 impl ValueSum {
+    pub(crate) fn zero() -> Self {
+        // Default for i64 is zero.
+        Default::default()
+    }
+
     /// Creates a value sum from its raw numeric value.
     ///
     /// This only enforces that the value is a signed 63-bit integer. Callers should