Fix handling of bytea-typed nulls

lib/Db/PostgreSQL/Result.php

@@ -49,7 +49,9 @@ class Result extends \JKingWeb\Arsse\Db\AbstractResult {
         $this->cur = pg_fetch_row($this->r, null, \PGSQL_ASSOC);
         if ($this->cur !== false) {
             foreach($this->blobs as $f) {
-                $this->cur[$f] = hex2bin(substr($this->cur[$f], 2));
+                if ($this->cur[$f]) {
+                    $this->cur[$f] = hex2bin(substr($this->cur[$f], 2));
+                }
             }
             return true;
         }

tests/cases/Db/BaseResult.php

@@ -11,6 +11,7 @@ use JKingWeb\Arsse\Db\Result;
 abstract class BaseResult extends \JKingWeb\Arsse\Test\AbstractTest {
     protected static $insertDefault = "INSERT INTO arsse_test default values";
     protected static $selectBlob = "SELECT x'DEADBEEF' as \"blob\"";
+    protected static $selectNullBlob = "SELECT null as \"blob\"";
     protected static $interface;
     protected $resultClass;
 
@@ -142,4 +143,15 @@ abstract class BaseResult extends \JKingWeb\Arsse\Test\AbstractTest {
         $test = new $this->resultClass(...$this->makeResult(static::$selectBlob));
         $this->assertEquals($exp, $test->getValue());
     }
+
+    public function testGetNullBlobRow(): void {
+        $exp = ['blob' => null];
+        $test = new $this->resultClass(...$this->makeResult(static::$selectNullBlob));
+        $this->assertEquals($exp, $test->getRow());
+    }
+
+    public function testGetNullBlobValue(): void {
+        $test = new $this->resultClass(...$this->makeResult(static::$selectNullBlob));
+        $this->assertNull($test->getValue());
+    }
 }

tests/cases/Db/PostgreSQL/TestResult.php

@@ -16,6 +16,7 @@ class TestResult extends \JKingWeb\Arsse\TestCase\Db\BaseResult {
     protected static $createMeta = "CREATE TABLE arsse_meta(key text primary key not null, value text)";
     protected static $createTest = "CREATE TABLE arsse_test(id bigserial primary key)";
     protected static $selectBlob = "SELECT '\\xDEADBEEF'::bytea as blob";
+    protected static $selectNullBlob = "SELECT null::bytea as blob";
 
     protected function makeResult(string $q): array {
         $set = pg_query(static::$interface, $q);

tests/cases/Db/PostgreSQLPDO/TestResult.php

@@ -16,6 +16,7 @@ class TestResult extends \JKingWeb\Arsse\TestCase\Db\BaseResult {
     protected static $createMeta = "CREATE TABLE arsse_meta(key text primary key not null, value text)";
     protected static $createTest = "CREATE TABLE arsse_test(id bigserial primary key)";
     protected static $selectBlob = "SELECT '\\xDEADBEEF'::bytea as blob";
+    protected static $selectNullBlob = "SELECT null::bytea as blob";
 
     protected function makeResult(string $q): array {
         $set = static::$interface->query($q);