Looks like certain version of Maven (2.2.1, 3.2.2 and 3.2.3) run into issues with com.google.code.gson:gson:2.3: google/gson#588
The issue is resolved in gson : 2.3.1.
The older version(2.3) is linked in google-cloud-core from grpc 1.0.3.
grpc 1.1+ support gson:2.7. Is there a reason not to be on atleast 1.1.x of grpc ?

[INFO] | | +- io.grpc:grpc-protobuf:jar:1.0.3:compile
[INFO] | | | +- (com.google.guava:guava:jar:19.0:compile - omitted for duplicate)
[INFO] | | | +- com.google.protobuf:protobuf-java-util:jar:3.0.2:compile
[INFO] | | | | +- (com.google.protobuf:protobuf-java:jar:3.0.2:compile - omitted for conflict with 3.0.0)
[INFO] | | | | +- (com.google.guava:guava:jar:18.0:compile - omitted for conflict with 20.0)
[INFO] | | | | - com.google.code.gson:gson:jar:2.3:compile