Fix to enum decoding behaviour

modules/core/src/main/scala/vulcan/Codec.scala

@@ -401,14 +401,13 @@ object Codec extends CodecCompanionCompat {
         else
           Left(AvroError.encodeSymbolNotInSchema(symbol, symbols, typeName))
       }, {
-        case (genericEnum: GenericEnumSymbol[_], schema) =>
-          val symbols = schema.getEnumSymbols().asScala.toList
+        case (genericEnum: GenericEnumSymbol[_], _) =>
           val symbol = genericEnum.toString()
 
           if (symbols.contains(symbol))
             decode(symbol)
           else
-            Left(AvroError.decodeSymbolNotInSchema(symbol, symbols, typeName))
+            default.toRight(AvroError.decodeSymbolNotInSchema(symbol, symbols, typeName))
       }
     )
   }

modules/core/src/test/scala/vulcan/CodecSpec.scala

@@ -597,14 +597,26 @@ final class CodecSpec extends BaseSpec with CodecSpecHelpers {
           )
         }
 
-        it("should error if encoded value is not a schema symbol") {
-          assertDecodeError[SealedTraitEnum](
+        it("should return default value if encoded value is not a schema symbol") {
+          assertDecodeIs[SealedTraitEnum](
             new GenericData.EnumSymbol(
               SchemaFactory.enumeration("vulcan.examples.SealedTraitEnum", Array("symbol")),
               "symbol"
             ),
+            Right(FirstInSealedTraitEnum),
+            Some(unsafeSchema[SealedTraitEnum])
+          )
+        }
+
+        it("should error if encoded value is not a schema symbol and there is no default value") {
+          assertDecodeError[SealedTraitEnumNoDefault](
+            new GenericData.EnumSymbol(
+              SchemaFactory
+                .enumeration("vulcan.examples.SealedTraitEnumNoDefault", Array("symbol")),
+              "symbol"
+            ),
             unsafeSchema[SealedTraitEnum],
-            "symbol is not part of schema symbols [first, second] for type vulcan.examples.SealedTraitEnum"
+            "symbol is not part of schema symbols [first, second] for type vulcan.examples.SealedTraitEnumNoDefault"
           )
         }
 

modules/core/src/test/scala/vulcan/examples/SealedTraitEnumNoDefault.scala

@@ -0,0 +1,39 @@
+package vulcan.examples
+
+import cats.Eq
+import org.scalacheck.{Arbitrary, Gen}
+import vulcan.{AvroError, Codec, Props}
+
+sealed trait SealedTraitEnumNoDefault
+
+object SealedTraitEnumNoDefault {
+  implicit final val arbitrary: Arbitrary[SealedTraitEnumNoDefault] =
+    Arbitrary(Gen.oneOf(FirstInSealedTraitEnumNoDefault, SecondInSealedTraitEnumNoDefault))
+
+  implicit final val eq: Eq[SealedTraitEnumNoDefault] =
+    Eq.fromUniversalEquals
+
+  implicit final val codec: Codec[SealedTraitEnumNoDefault] =
+    Codec.enumeration(
+      name = "SealedTraitEnumNoDefault",
+      namespace = "vulcan.examples",
+      symbols = List("first", "second"),
+      aliases = List("first", "second"),
+      doc = Some("documentation"),
+      default = None,
+      encode = {
+        case FirstInSealedTraitEnumNoDefault  => "first"
+        case SecondInSealedTraitEnumNoDefault => "second"
+      },
+      decode = {
+        case "first"  => Right(FirstInSealedTraitEnumNoDefault)
+        case "second" => Right(SecondInSealedTraitEnumNoDefault)
+        case other    => Left(AvroError(other))
+      },
+      props = Props.one("custom1", 10).add("custom2", "value2")
+    )
+}
+
+case object FirstInSealedTraitEnumNoDefault extends SealedTraitEnumNoDefault
+
+case object SecondInSealedTraitEnumNoDefault extends SealedTraitEnumNoDefault