Minor bug fixes for SastBuildActions

The stage parameter should be a string, not a symbol
The call to .compact doesn't remove empty strings, and we don't want to
write variables to the YML that don't have a value set.

ee/lib/security/ci_configuration/sast_build_actions.rb

@@ -36,12 +36,14 @@ module Security
       end
 
       def sast_stage
-        @params[:stage] || 'test'
+        @params['stage'] || 'test'
       end
 
       # We only want to write variables that are set
       def parse_variables(variables)
-        variables.map { |var| [var, @params[var]] }.to_h.compact
+        variables.map { |var| [var, @params[var]] }
+                 .to_h
+                 .select { |k, v| v.present? }
       end
 
       def sast_block

ee/spec/lib/security/ci_configuration/sast_build_actions_spec.rb

@@ -6,8 +6,8 @@ RSpec.describe Security::CiConfiguration::SastBuildActions do
   context 'autodevops disabled' do
     let(:auto_devops_enabled) { false }
 
-    context 'with no paramaters' do
-      let(:params) { {} }
+    context 'with one empty parameter' do
+      let(:params) { { 'SECURE_ANALYZERS_PREFIX' => '' } }
 
       subject(:result) { described_class.new(auto_devops_enabled, params).generate }
 
@@ -18,7 +18,7 @@ RSpec.describe Security::CiConfiguration::SastBuildActions do
 
     context 'with all parameters' do
       let(:params) do
-        { stage: 'security',
+        { 'stage' => 'security',
           'SEARCH_MAX_DEPTH' => 1,
           'SECURE_ANALYZERS_PREFIX' => 'localhost:5000/analyzers',
           'SAST_ANALYZER_IMAGE_TAG' => 2,
@@ -35,7 +35,7 @@ RSpec.describe Security::CiConfiguration::SastBuildActions do
 
   context 'with autodevops enabled' do
     let(:auto_devops_enabled) { true }
-    let(:params) { { stage: 'custom stage' } }
+    let(:params) { { 'stage' => 'custom stage' } }
 
     subject(:result) { described_class.new(auto_devops_enabled, params).generate }