Fix avro serialization of union types

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Unreleased
 
+- Fixed a bug with avro serialization, where default values within a union type would not be used correctly.
+
 ### [0.9.12] - [2023-12-05]
 - Support for Foreign Key joins [#365](https://github.com/FundingCircle/jackdaw/pull/365) (Issue [#364])
 - add manifold and keep aleph in dev dependencies [#360](https://github.com/FundingCircle/jackdaw/pull/360). Users of test-machine will have to add aleph to the test deps in their app.

src/jackdaw/serdes/avro.clj

@@ -402,7 +402,7 @@
       (and (every? (fn [[field-key [^Schema$Field field field-coercion]]]
                      (let [field-value (get clj-map field-key ::missing)]
                        (if (= field-value ::missing)
-                         (.defaultVal field)
+                         (.hasDefaultValue field)
                          (match-clj? field-coercion field-value))))
                    field->schema+coercion)
            (empty? unknown-fields))))

test/jackdaw/serdes/avro_test.clj

@@ -463,6 +463,21 @@
     (is (= {:myunion {:field2 "hello"}}
            (round-trip serde "whatever" {:myunion {:field2 "hello"}})))))
 
+(deftest default-values-are-used-when-coercing-union-record
+  (let [schema {:type   "record",
+                :name   "myrecord",
+                :fields [{:name "myunion",
+                          :type [{:type   :null}
+                                 {:type   "record",
+                                  :name   "recordtype",
+                                  :fields [{:name "foo"
+                                            :type "boolean"
+                                            :default false}]}]}]}
+        serde  (->serde (json/write-str schema))]
+
+    (is (= {:myunion {:foo false}}
+           (round-trip serde "whatever" {:myunion {}})))))
+
 (deftest record-serde-test
   (let [serde (->serde complex-schema-str)
         valid-map {:string-field "hello"