lookup_header
  
  Description:
  public unowned string lookup_header (
string header)
  
 
  
    Get the value of the header called header.
    Parameters:
    
      
        | this | The ProxyCall | 
      
        | header | The header name | 
    
    Returns:
    
      
        | The header value, or nullif it does not exist. This string is owned by the 
            ProxyCall and should not be freed. |