[Metadata] Add exception message for when metadata object is null

Bug: b/276430511
Change-Id: I5d4b42ead491c0afab49e2915805e961ed6fd28b

src/main/java/com/android/tools/r8/kotlin/KotlinClassMetadataReader.java

diff --git a/src/main/java/com/android/tools/r8/kotlin/KotlinClassMetadataReader.java b/src/main/java/com/android/tools/r8/kotlin/KotlinClassMetadataReader.java
index a9d515a..d63d8e7 100644
--- a/src/main/java/com/android/tools/r8/kotlin/KotlinClassMetadataReader.java
+++ b/src/main/java/com/android/tools/r8/kotlin/KotlinClassMetadataReader.java
@@ -95,7 +95,8 @@
     Kotlin kotlin = appView.dexItemFactory().kotlin;
     KotlinClassMetadata kMetadata = toKotlinClassMetadata(kotlin, annotation.annotation);
     if (kMetadata == null) {
-      throw new KotlinMetadataException();
+      throw new KotlinMetadataException(
+          new Exception("Could not parse metadata for " + clazz.toSourceString()));
     }
     return createKotlinInfo(kotlin, clazz, kMetadata, appView, keepByteCode);
   }