Remove duplicated validation in branch and link package step

The super class of the steps already takes care of validating
the presence of the source package and source project names through
the REQUIRED_KEYS constant.
Additionally we have to add a validation to check for the
presence of the value for a required key.

src/api/app/models/workflow/step.rb

@@ -39,14 +39,23 @@ def create_or_update_subscriptions(package, workflow_filters)
 
   def validate_step_instructions
     self.class::REQUIRED_KEYS.each do |required_key|
-      errors.add(:base, "The '#{required_key}' key is missing") unless step_instructions.key?(required_key)
+      unless step_instructions.key?(required_key)
+        errors.add(:base, "The '#{required_key}' key is missing")
+        next
+      end
+
+      errors.add(:base, "The '#{required_key}' key must provide a value") if step_instructions[required_key].blank?
     end
   end
 
   def source_package_name
     step_instructions[:source_package]
   end
 
+  def source_project_name
+    step_instructions[:source_project]
+  end
+
   def target_package_name
     return step_instructions[:target_package] if step_instructions[:target_package].present?
 

src/api/app/models/workflow/step/branch_package_step.rb

@@ -1,20 +1,13 @@
 class Workflow::Step::BranchPackageStep < ::Workflow::Step
   REQUIRED_KEYS = [:source_project, :source_package].freeze
 
-  validates :source_project_name, presence: true
-  validates :source_package_name, presence: true
-
   def call(options = {})
     return unless valid?
 
     workflow_filters = options.fetch(:workflow_filters, {})
     branch_package(workflow_filters)
   end
 
-  def source_project_name
-    step_instructions[:source_project]
-  end
-
   private
 
   def branch_package(workflow_filters = {})

src/api/app/models/workflow/step/link_package_step.rb

@@ -1,20 +1,13 @@
 class Workflow::Step::LinkPackageStep < ::Workflow::Step
   REQUIRED_KEYS = [:source_project, :source_package].freeze
 
-  validates :source_project_name, presence: true
-  validates :source_package_name, presence: true
-
   def call(options = {})
     return unless valid?
 
     workflow_filters = options.fetch(:workflow_filters, {})
     link_package(workflow_filters)
   end
 
-  def source_project_name
-    step_instructions[:source_project]
-  end
-
   private
 
   def link_package(workflow_filters = {})

src/api/spec/validators/workflow_steps_validator_spec.rb

@@ -51,7 +51,7 @@
       it 'is not valid and has an error message' do
         subject.valid?
         expect(subject.errors.full_messages.to_sentence).to eq("The following workflow steps are unsupported: 'unsupported_step' and " \
-                                                               "The 'source_package' key is missing and Source package name can't be blank")
+                                                               "The 'source_package' key is missing")
       end
     end
   end