code: private Icon getIcon( Severity severity ) {
          if( severity == Severity.ERROR ) {
              return getErrorIcon();
          }
          if( severity == Severity.WARNING ) {
              return getWarningIcon();
          }
          return getInfoIcon();
      }
docs: Returns the icon for the given severity.
  @param severity The severity level.
  @return The icon for the given severity, never null.