add fn deserialize_null_as_default for deserializing JSON null values

sdk/core/src/util.rs

@@ -15,3 +15,55 @@ where
         .or_else(|_| T::deserialize(serde_json::Value::String(v.to_lowercase())))
         .map_err(de::Error::custom)
 }
+
+/// Deserialize JSON null as default
+/// https://github.com/serde-rs/serde/issues/1098
+pub fn deserialize_null_as_default<'de, D, T>(deserializer: D) -> Result<T, D::Error>
+where
+    T: Default + Deserialize<'de>,
+    D: Deserializer<'de>,
+{
+    let opt = Option::deserialize(deserializer)?;
+    Ok(opt.unwrap_or_default())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde::Serialize;
+
+    #[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Default)]
+    pub struct SiteConfig {
+        #[serde(
+            rename = "appSettings",
+            default,
+            deserialize_with = "deserialize_null_as_default",
+            skip_serializing_if = "Vec::is_empty"
+        )]
+        pub app_settings: Vec<NameValuePair>,
+    }
+
+    #[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Default)]
+    pub struct NameValuePair {
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        pub name: Option<String>,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        pub value: Option<String>,
+    }
+
+    #[test]
+    fn deserialize_empty() -> crate::Result<()> {
+        let bytes = br#"{}"#;
+        let site_config: SiteConfig = serde_json::from_slice(bytes)?;
+        assert_eq!(Vec::<NameValuePair>::default(), site_config.app_settings);
+        Ok(())
+    }
+
+    #[test]
+    fn deserialize_null() -> crate::Result<()> {
+        let bytes = br#"{ "appSettings": null }"#;
+        let site_config: SiteConfig = serde_json::from_slice(bytes)?;
+        assert_eq!(Vec::<NameValuePair>::default(), site_config.app_settings);
+        Ok(())
+    }
+}

services/autorust/codegen/src/codegen_models.rs

@@ -707,7 +707,7 @@ fn create_struct(cg: &CodeGen, schema: &SchemaGen, struct_name: &str, pageable:
                 // Must specify `default` when using `with` for `Option`
                 serde_attrs.push(quote! { default, with = "azure_core::date::rfc1123::option"});
             } else if type_name.is_vec() {
-                serde_attrs.push(quote! { default, skip_serializing_if = "Vec::is_empty"});
+                serde_attrs.push(quote! { default, deserialize_with = "azure_core::util::deserialize_null_as_default", skip_serializing_if = "Vec::is_empty"});
             } else {
                 serde_attrs.push(quote! { default, skip_serializing_if = "Option::is_none"});
             }