public void testEmptyOperatorOnStrings() {
    ParserConfiguration conf = new ParserConfiguration();
    ParserContext pctx = new ParserContext( conf );
    pctx.setStrictTypeEnforcement(true);
    pctx.setStrongTyping(true);

    pctx.addInput("nullString", String.class);
    pctx.addInput("emptyString", String.class);
    pctx.addInput("blankString", String.class);
    pctx.addInput("nonEmptyString", String.class);
    Map vars = new HashMap() {{
        put("nullString", null);
        put("emptyString", "");
        put("blankString", "   ");
        put("nonEmptyString", "abc");
    }};

    assertEquals(true, MVEL.executeExpression(MVEL.compileExpression("nullString == empty", pctx), vars));
    assertEquals(true, MVEL.executeExpression(MVEL.compileExpression("emptyString == empty", pctx), vars));
    assertEquals(true, MVEL.executeExpression(MVEL.compileExpression("blankString == empty", pctx), vars));
    assertEquals(false, MVEL.executeExpression(MVEL.compileExpression("nonEmptyString == empty", pctx), vars));
  }