fix(gapic-common): Fixed handling of optional fields in coerce (#954)

Author: psyho

gapic-common/lib/gapic/protobuf.rb

@@ -31,6 +31,7 @@ module Protobuf
     # @return [Object] An instance of the given message class.
     def self.coerce hash, to:
       return hash if hash.is_a? to
+      return nil if hash.nil?
 
       # Special case handling of certain types
       return time_to_timestamp hash if to == Google::Protobuf::Timestamp && hash.is_a?(Time)

gapic-common/test/gapic/protobuf/coerce_test.rb

@@ -35,6 +35,15 @@ class ProtobufCoerceTest < Minitest::Spec
     _(user.type).must_equal USER_TYPE
   end
 
+  it "handles optional fields in a simple hash" do
+    hash = { name: USER_NAME, type: USER_TYPE, timestamp: nil }
+    user = Gapic::Protobuf.coerce hash, to: Gapic::Examples::User
+    _(user).must_be_kind_of Gapic::Examples::User
+    _(user.name).must_equal USER_NAME
+    _(user.type).must_equal USER_TYPE
+    _(user.timestamp).must_be_nil
+  end
+
   it "creates a protobuf message from a hash with a nested message" do
     request_hash = { name: REQUEST_NAME, user: Gapic::Examples::User.new(name: USER_NAME, type: USER_TYPE) }
     request = Gapic::Protobuf.coerce request_hash, to: Gapic::Examples::Request