code: public static void isTrue (@Nonnull final BooleanSupplier aValue, @Nonnull final Supplier <? extends String> aMsg)
    {
      if (isEnabled ())
        if (!aValue.getAsBoolean ())
          throw new IllegalArgumentException ("The expression must be true but it is not: " + aMsg.get ());
    }
docs: Check that the passed value is <code>true</code>.
  
  @param aValue
  The value to check.
  @param aMsg
  The message to be emitted in case the value is <code>false</code>
  @throws IllegalArgumentException
  if the passed value is not <code>null</code>.