unionWith example

public function specifyTypes(MethodReflection $methodReflection, MethodCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
    {
        $getExpr = new MethodCall($node->var, 'get', $node->args);

        $getterTypes = $this->typeSpecifier->create(
            $getExpr,
            TypeCombinator::removeNull($scope->getType($getExpr)),
            $context
        );

        return $getterTypes->unionWith(
            $this->typeSpecifier->create(
                $getExpr,
                new NullType(),
                $context->negate()
            )
        );
    }

    public function setTypeSpecifier(TypeSpecifier $typeSpecifier): void
    {
        $this->typeSpecifier = $typeSpecifier;
    }