Make it a fatal error if no source files for Java module.

Change-Id: Ia04158c11381b6b1687b9d5c699a9ea8ae3cb317
diff --git a/core/base_rules.mk b/core/base_rules.mk
index 87df472..3d5f51d 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -354,7 +354,7 @@
 
 ## PRIVATE java vars ######################################
 
-ifneq ($(strip $(all_java_sources)$(all_res_assets))$(LOCAL_STATIC_JAVA_LIBRARIES),)
+ifneq ($(strip $(all_java_sources)$(all_res_assets))$(LOCAL_STATIC_JAVA_LIBRARIES)$(filter true,$(LOCAL_SOURCE_FILES_ALL_GENERATED)),)
 
 full_static_java_libs := \
     $(foreach lib,$(LOCAL_STATIC_JAVA_LIBRARIES), \