Avoid using a null alias as an array offset in getAliases()

SelectStatement::getAliases() built a table-alias map with
`$tables[$thisDb][$expr->alias] = $expr->table` for every FROM/JOIN
expression. When a table has no alias, `$expr->alias` is null, so this
used null as an array offset, which is deprecated as of PHP 8.5
("Using null as an array offset is deprecated, use an empty string
instead"). The null-keyed entry was never read back either: the only
consumer looks up `$tables[$thisDb][$expr->table]`, whose offset is
always a non-empty string.

Skip expressions without an alias, mirroring the existing
`isset($expr->alias) && $expr->alias !== ''` checks above. getAliases()
output is unchanged. Removes the now-resolved PossiblyNullArrayOffset
entry from the Psalm baseline and adds a regression test.

Author: ardittirana

psalm-baseline.xml

@@ -806,7 +806,6 @@
       <code><![CDATA[array<string, array<string, array<string, array<string, array<string, string>|string|null>>|null>>]]></code>
     </MixedReturnTypeCoercion>
     <PossiblyNullArrayOffset>
-      <code><![CDATA[$tables[$thisDb]]]></code>
       <code><![CDATA[Parser::STATEMENT_PARSERS]]></code>
     </PossiblyNullArrayOffset>
     <PossiblyUnusedProperty>

src/Statements/SelectStatement.php

@@ -607,6 +607,13 @@ public function getAliases(string $database): array
                 ];
             }
 
+            // Only record an alias => table mapping when an alias exists.
+            // Using a null alias as an array offset is deprecated as of
+            // PHP 8.5, and such an entry is never read back below anyway.
+            if (! isset($expr->alias) || ($expr->alias === '')) {
+                continue;
+            }
+
             if (! isset($tables[$thisDb])) {
                 $tables[$thisDb] = [];
             }

tests/Builder/StatementTest.php

@@ -155,6 +155,28 @@ public static function getAliasesProvider(): array
                     ],
                 ],
             ],
+            [
+                // An unaliased table alongside an aliased one. The unaliased
+                // table must not break alias resolution; previously its null
+                // alias was used as an array offset (deprecated in PHP 8.5).
+                'SELECT mytable.a x, o.b y FROM mytable JOIN other o ON o.id = mytable.id',
+                'shop',
+                [
+                    'shop' => [
+                        'alias' => null,
+                        'tables' => [
+                            'mytable' => [
+                                'alias' => null,
+                                'columns' => ['a' => 'x'],
+                            ],
+                            'other' => [
+                                'alias' => 'o',
+                                'columns' => ['b' => 'y'],
+                            ],
+                        ],
+                    ],
+                ],
+            ],
         ];
     }
 }