fix: Allow Docker Secrets to override empty environment variables

- Update get() method to treat empty strings as 'not set' for Docker Secrets resolution
- Allows Docker Secrets (*_FILE pattern) to override empty values
- Preserves original behavior: explicitly set empty strings are still returned
- Fixes issue where RAPIDMAIL_USERNAME and RAPIDMAIL_PASSWORD appear empty even when Docker Secrets are available

src/Framework/Config/Environment.php

@@ -23,12 +23,19 @@ final readonly class Environment
     {
         $key = $this->keyToString($key);
 
-        // 1. Check if direct env var exists in internal array
+        // 1. Check if direct env var exists in internal array and is not empty
+        // Empty strings are treated as "not set" to allow Docker Secrets resolution
         if (isset($this->variables[$key])) {
-            return $this->variables[$key];
+            $value = $this->variables[$key];
+            // If value is not empty, return it (non-empty values take precedence)
+            if ($value !== '' && $value !== null) {
+                return $value;
+            }
+            // If value is empty, continue to check Docker Secrets as fallback
         }
 
         // 2. Docker Secrets support: Check for *_FILE pattern
+        // This allows Docker Secrets to override empty values
         $secretValue = $this->secretsResolver->resolve($key, $this->variables);
         if ($secretValue !== null) {
             return $secretValue;
@@ -38,11 +45,17 @@ final readonly class Environment
         // This handles cases where environment variables are set after Environment initialization
         // (common in PHP-FPM where vars may be set during request processing)
         $systemValue = $this->getFromSystemEnvironment($key);
-        if ($systemValue !== null) {
+        if ($systemValue !== null && $systemValue !== '') {
             return $systemValue;
         }
 
-        // 4. Return default
+        // 4. If internal variable was set (even if empty), return it (to distinguish between "not set" and "empty")
+        // This preserves the original behavior: if variable is explicitly set to empty string, return it
+        if (isset($this->variables[$key])) {
+            return $this->variables[$key];
+        }
+
+        // 5. Return default
         return $default;
     }