Tweak

src/convert.rs

@@ -134,6 +134,16 @@ impl<T: ToBytesGadget<F>, F: Field, const N: usize> ToBytesGadget<F> for [T; N]
     }
 }
 
+impl<F: Field> ToBytesGadget<F> for () {
+    fn to_bytes_le(&self) -> Result<Vec<UInt8<F>>, SynthesisError> {
+        Ok(Vec::new())
+    }
+
+    fn to_non_unique_bytes_le(&self) -> Result<Vec<UInt8<F>>, SynthesisError> {
+        Ok(Vec::new())
+    }
+}
+
 /// Specifies how to convert a variable of type `Self` to variables of
 /// type `FpVar<ConstraintF>`
 pub trait ToConstraintFieldGadget<ConstraintF: ark_ff::PrimeField> {

src/eq.rs

@@ -86,7 +86,7 @@ impl<T: EqGadget<F> + R1CSVar<F>, F: PrimeField> EqGadget<F> for [T] {
     #[tracing::instrument(target = "r1cs", skip(self, other))]
     fn is_eq(&self, other: &Self) -> Result<Boolean<F>, SynthesisError> {
         assert_eq!(self.len(), other.len());
-        if self.is_empty() {
+        if self.is_empty() & other.is_empty() {
             Ok(Boolean::TRUE)
         } else {
             let mut results = Vec::with_capacity(self.len());