fix(solc): emit empty vec for empty artifacts

ethers-solc/src/artifact_output/configurable.rs

@@ -337,6 +337,7 @@ impl ArtifactOutput for ConfigurableArtifacts {
         file: &VersionedSourceFile,
     ) -> Option<Self::Artifact> {
         file.source_file.ast.clone().map(|ast| ConfigurableContractArtifact {
+            abi: Some(LosslessAbi::default()),
             id: Some(file.source_file.id),
             ast: Some(ast),
             bytecode: Some(CompactBytecode::empty()),

ethers-solc/src/artifacts/mod.rs

@@ -1318,14 +1318,20 @@ impl OutputContracts {
 /// ethabi as it would require a redesign of the overall `Param` and `ParamType` types. Instead,
 /// this type keeps a copy of the [`serde_json::Value`] when deserialized from the `solc` json
 /// compiler output and uses it to serialize the `abi` without loss.
-#[derive(Clone, Debug, PartialEq, Default)]
+#[derive(Clone, Debug, PartialEq)]
 pub struct LosslessAbi {
     /// The complete abi as json value
     pub abi_value: serde_json::Value,
     /// The deserialised version of `abi_value`
     pub abi: Abi,
 }
 
+impl Default for LosslessAbi {
+    fn default() -> Self {
+        LosslessAbi { abi_value: serde_json::json!([]), abi: Default::default() }
+    }
+}
+
 impl From<LosslessAbi> for Abi {
     fn from(abi: LosslessAbi) -> Self {
         abi.abi