Refactor SelectTree formatting and minor logic improvements

Removed redundant blank lines and refined spacing for better code readability. Adjusted conditional key assignment logic to ensure consistent formatting without altering functionality.

Author: lotestudio

src/SelectTree.php

@@ -312,7 +312,6 @@ public function prepend(Closure|array|null $prepend = null): static
         return $this;
     }
 
-
     public function getRelationship(): BelongsToMany|BelongsTo
     {
         return $this->getModelInstance()->{$this->evaluate($this->relationship)}();
@@ -450,7 +449,7 @@ public function getIndependent(): bool
 
     public function getCustomKey($record): string
     {
-        $key =  is_null($this->customKey) ? $record->getKey() : $record->{$this->customKey};
+        $key = is_null($this->customKey) ? $record->getKey() : $record->{$this->customKey};
 
         return (string) $key;
     }