code: private Object getPropertyValue(GDLParser.LiteralContext literalContext) {
      String text;
      if (literalContext.StringLiteral() != null) {
        return parseString(literalContext.StringLiteral().getText());
      } else if (literalContext.BooleanLiteral() != null) {
        return Boolean.parseBoolean(literalContext.BooleanLiteral().getText());
      } else if (literalContext.IntegerLiteral() != null) {
        text = literalContext.IntegerLiteral().getText().toLowerCase();
        if (text.endsWith("l")) {
          return Long.parseLong(text.substring(0, text.length() - 1));
        }
        return Integer.parseInt(text);
      } else if (literalContext.FloatingPointLiteral() != null) {
        text = literalContext.FloatingPointLiteral().getText().toLowerCase();
        if (text.endsWith("f")) {
          return Float.parseFloat(text.substring(0, text.length() - 1));
        } else if (text.endsWith("d")) {
          return Double.parseDouble(text.substring(0, text.length() - 1));
        }
        return Float.parseFloat(text);
      }
      return null;
    }
docs: Returns the corresponding value for a given literal.
  
  @param literalContext literal context
  @return parsed value