Use valid schema related to null default based on specification in

RecordEvolutionTest

during investigation upgrading Avro to 1.9+, the test was failing. the
code has enforced the rule from the specification that `when a default
value is specified for a record field whose type is a union, the type of
the default value must match the first element of the union. Thus, for
unions containing "null", the "null" is usually listed first, since the
default value of such unions is typically null.`

it was part of specification in 1.8 already
https://avro.apache.org/docs/1.8.0/spec.html#Unions , just not enforced
in the codebase.

relates to FasterXML#167

Signed-off-by: Aurélien Pupier <[email protected]>

Author: apupier

avro/src/test/java/com/fasterxml/jackson/dataformat/avro/schemaev/RecordEvolutionTest.java

@@ -17,7 +17,7 @@ public class RecordEvolutionTest extends AvroTestBase
         + " \"fields\": [\n"
         + "     {\n"
         + "        \"name\": \"name\",\n"
-        + "        \"type\": [\"string\", \"null\"],\n"
+        + "        \"type\": [\"null\", \"string\"],\n"
         + "        \"default\": null\n"
         + "    },\n"
         + "     {\n"
@@ -39,7 +39,7 @@ public class RecordEvolutionTest extends AvroTestBase
         + " \"fields\": [\n"
         + "     {\n"
         + "        \"name\": \"fullName\",\n"
-        + "        \"type\": [\"string\", \"null\"],\n"
+        + "        \"type\": [\"null\", \"string\"],\n"
         + "        \"default\": null,\n"
         + "        \"aliases\": [\"name\"]\n"
         + "    },\n"