[Java] Fix key lookup returning null clashing with default value (#7236)

A field with key attribute must always be written on the message so it
can be looked up by key. There is a edge case where inserting a key
field with same value as default would prevent it to be written on
the message and later cannot be found when searched by key.

scripts/generate_code.py

@@ -362,6 +362,10 @@ flatc(
 )
 flatc(BASE_OPTS + DART_OPTS, prefix="../dart/test/", schema="keyword_test.fbs")
 
+# Field key lookup with default value test
+dictionary_lookup_schema = "dictionary_lookup.fbs"
+flatc(["--java"], schema=dictionary_lookup_schema)
+
 # Swift Tests
 swift_prefix = "FlatBuffers.Test.Swift/Tests/FlatBuffers.Test.SwiftTests"
 flatc(