Start bazel support for protobuf models and p4runtime build

Change-Id: Ib3beb70c1b401854444b106b4af3723cd40635e4
diff --git a/tools/build/bazel/osgi-java-library.bzl b/tools/build/bazel/osgi-java-library.bzl
index e47c3d7..c3ed9b3 100644
--- a/tools/build/bazel/osgi-java-library.bzl
+++ b/tools/build/bazel/osgi-java-library.bzl
@@ -36,6 +36,9 @@
 
     # determine the dependencies and build the class path
     for dep in ctx.attr.deps:
+        if len(dep.java.outputs.jars) == 0:
+            continue
+
         file = dep.java.outputs.jars[0].class_jar
 
         if cp: