Java Obsfucate Password - Replace with asterisk

Obsfucate password : 

Rreplace everything except first and last character by asterisk ( * ), if  the password is less than ALLOWED_LENGTH characters long obfuscate it entirely i.e., prints asterisks

Code :

   
//Test 
System.out.println( getObfuscatedPassword( "" ) ); //returns null
System.out.println( getObfuscatedPassword( "pwdd" ) ); //returns ****
System.out.println( getObfuscatedPassword( "mySecurePassword" ) ); // returns m**************d


//Method 
public static String getObfuscatedPassword( String password ) {
   
   int ALLOWED_LENGTH = 5;
   
   if ( null == password || "".equals( password.trim( ) ) ) {
    return null;
   }
   
   StringBuilder builder = new StringBuilder( );
   
   if ( password.length( ) < ALLOWED_LENGTH ) {
   
    for ( int i = password.length( ); i != 0; i-- ) {
     builder.append( "*" );
    }
   
    return builder.toString( );
   }
   
   builder.append( password.charAt( 0 ) );
   
   for ( int i = password.length( ) - 2; i != 0; i-- ) {
    builder.append( "*" );
   }
   
   return builder.append( password.substring( password.length( ) - 1 ) ).toString( );
}