diff --git a/src/FactorGraphs/FactorGraph.php b/src/FactorGraphs/FactorGraph.php
index 8698bb7..c07bc4f 100644
--- a/src/FactorGraphs/FactorGraph.php
+++ b/src/FactorGraphs/FactorGraph.php
@@ -4,10 +4,15 @@ declare(strict_types=1);
 
 namespace DNW\Skills\FactorGraphs;
 
-class FactorGraph
+abstract class FactorGraph
 {
     private VariableFactory $variableFactory;
 
+    protected function __construct()
+    {
+        $this->variableFactory = new VariableFactory(fn () => NULL);
+    }
+
     public function getVariableFactory(): VariableFactory
     {
         return $this->variableFactory;
diff --git a/src/TrueSkill/Layers/PlayerPerformancesToTeamPerformancesLayer.php b/src/TrueSkill/Layers/PlayerPerformancesToTeamPerformancesLayer.php
index 8576477..0ed6f33 100644
--- a/src/TrueSkill/Layers/PlayerPerformancesToTeamPerformancesLayer.php
+++ b/src/TrueSkill/Layers/PlayerPerformancesToTeamPerformancesLayer.php
@@ -18,6 +18,9 @@ class PlayerPerformancesToTeamPerformancesLayer extends TrueSkillFactorGraphLaye
     public function buildLayer(): void
     {
         $inputVariablesGroups = $this->getInputVariablesGroups();
+        /**
+         * @var KeyedVariable[] $currentTeam
+         */
         foreach ($inputVariablesGroups as $currentTeam) {
             $localCurrentTeam = $currentTeam;
             $teamPerformance = $this->createOutputVariable($localCurrentTeam);
diff --git a/src/TrueSkill/TrueSkillFactorGraph.php b/src/TrueSkill/TrueSkillFactorGraph.php
index 495c4ef..0be279c 100644
--- a/src/TrueSkill/TrueSkillFactorGraph.php
+++ b/src/TrueSkill/TrueSkillFactorGraph.php
@@ -37,6 +37,7 @@ class TrueSkillFactorGraph extends FactorGraph
      */
     public function __construct(private readonly GameInfo $gameInfo, array $teams, array $teamRanks)
     {
+        parent::__construct();
         $this->priorLayer = new PlayerPriorValuesToSkillsLayer($this, $teams);
         $newFactory = new VariableFactory(
             static fn(): GaussianDistribution => GaussianDistribution::fromPrecisionMean(0, 0)