chore: Fix Lint/SafeNavigationWithEmpty RuboCop warnings (#1302)

Author: aandreassa

gapic-generator/lib/gapic/presenters/sample_presenter.rb

@@ -69,7 +69,7 @@ def initialize field
           @value = convert field["value"]
           @input_parameter = field["input_parameter"]
           @comment = field["comment"]
-          @comment = nil if @comment&.empty?
+          @comment = nil if @comment && @comment.empty?
           @value_is_file = field["value_is_file"]
         end
 

gapic-generator/lib/gapic/presenters/snippet/parameter_presenter.rb

@@ -33,7 +33,7 @@ class ParameterPresenter
         def initialize proto, json
           @name = proto.name
           @description = proto.description
-          @description = nil if @description&.empty?
+          @description = nil if @description && @description.empty?
           @type = TypePresenter.new proto&.type, json&.fetch("type", nil)
           @example = ExpressionPresenter.new proto&.value, json&.fetch("value", nil)
         end