Fix GH-23758: PDO_Firebird returns null for empty BLOBs

NEWS

@@ -32,6 +32,10 @@ PHP                                                                        NEWS
   . Fixed PDOStatement::getColumnMeta() reading out of bounds for an invalid
     column index. (Ilia Alshanetsky)
 
+- PDO_Firebird:
+  . Fixed bug GH-23758 (PDO_Firebird returns null for non-null empty BLOBs).
+    (Lazizbek Ergashev)
+
 - Sockets:
   . Fixed socket_select() silently truncating sets larger than FD_SETSIZE on
     Windows. (David Carlier)

ext/pdo_firebird/firebird_statement.c

@@ -446,6 +446,8 @@ static int php_firebird_fetch_blob(pdo_stmt_t *stmt, int colno, zval *result, IS
 			php_firebird_error_stmt_with_info(stmt, "HY000", strlen("HY000"), msg, strlen(msg));
 			goto fetch_blob_end;
 		}
+	} else {
+		ZVAL_EMPTY_STRING(result);
 	}
 	retval = 1;
 

ext/pdo_firebird/tests/gh23758.phpt

@@ -0,0 +1,52 @@
+--TEST--
+GH-23758 (PDO_Firebird returns null for non-null empty BLOBs)
+--EXTENSIONS--
+pdo_firebird
+--SKIPIF--
+<?php require('skipif.inc'); ?>
+--XLEAK--
+A bug in firebird causes a memory leak when calling `isc_attach_database()`.
+See https://github.com/FirebirdSQL/firebird/issues/7849
+--FILE--
+<?php
+
+require("testdb.inc");
+
+$dbh = getDbConnection();
+$dbh->exec('CREATE TABLE gh23758 (ID INTEGER, BIN_VAL BLOB SUB_TYPE BINARY, TEXT_VAL BLOB SUB_TYPE TEXT)');
+
+$stmt = $dbh->prepare('INSERT INTO gh23758 VALUES (?, ?, ?)');
+$stmt->execute([1, null, null]);
+$stmt->execute([2, '', '']);
+
+$stmt = $dbh->query('SELECT BIN_VAL, TEXT_VAL FROM gh23758 ORDER BY ID');
+var_dump($stmt->fetchAll(PDO::FETCH_NUM));
+
+unset($stmt);
+unset($dbh);
+
+?>
+--CLEAN--
+<?php
+require 'testdb.inc';
+$dbh = getDbConnection();
+@$dbh->exec('DROP TABLE gh23758');
+unset($dbh);
+?>
+--EXPECT--
+array(2) {
+  [0]=>
+  array(2) {
+    [0]=>
+    NULL
+    [1]=>
+    NULL
+  }
+  [1]=>
+  array(2) {
+    [0]=>
+    string(0) ""
+    [1]=>
+    string(0) ""
+  }
+}