I got an unexpected internal NPE when playing with this script.

```
POST _scripts/painless/_execute
{
  "script": {
    "source": """
    return /[^\w]+/.split('abc   def higkln').toArray(String[]::new)
    """
  }
}
```
```
{
  "error" : {
    "root_cause" : [
      {
        "type" : "script_exception",
        "reason" : "compile error",
        "script_stack" : [ ],
        "script" : "\n    return /[^\\w]+/.split('abc   def higkln').toArray(String[]::new)\n    ",
        "lang" : "painless"
      }
    ],
    "type" : "script_exception",
    "reason" : "compile error",
    "script_stack" : [ ],
    "script" : "\n    return /[^\\w]+/.split('abc   def higkln').toArray(String[]::new)\n    ",
    "lang" : "painless",
    "caused_by" : {
      "type" : "null_pointer_exception",
      "reason" : "Cannot read field \"annotations\" because the return value of \"org.elasticsearch.painless.lookup.PainlessLookup.lookupPainlessClass(java.lang.Class)\" is null"
    }
  },
  "status" : 400
}

```
modules/lang-painless/src/test/java/org/elasticsearch/painless/WhenThingsGoWrongTests.java
IllegalArgumentException.class,
            () -> exec("java.util.List[] x = new java.util.List[1]; x[java.util.List]")
        );
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");
        
        iae = expectScriptThrows(IllegalArgumentException.class, () -> exec("java.util.List ?: []"));
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");
        iae = expectScriptThrows(IllegalArgumentException.class, () -> exec("boolean x = true; x ?: java.util.List"));
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");
        
        iae = expectScriptThrows(IllegalArgumentException.class, () -> exec("(java.util.List)java.util.List"));
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");
        
        iae = expectScriptThrows(IllegalArgumentException.class, () -> exec("java.util.List instanceof java.util.List"));
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");
        
        iae = expectScriptThrows(IllegalArgumentException.class, () -> exec("[java.util.List]"));
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");
        
        iae = expectScriptThrows(IllegalArgumentException.class, () -> exec("[java.util.List : 1]"));
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");
        iae = expectScriptThrows(IllegalArgumentException.class, () -> exec("[1 : java.util.List]"));
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");
        
        iae = expectScriptThrows(IllegalArgumentException.class, () -> exec("new java.util.List[java.util.List]"));
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");
        
        iae = expectScriptThrows(IllegalArgumentException.class, () -> exec("new java.util.ArrayList(java.util.List)"));
        assertEquals(iae.getMessage(), "value required: instead found unexpected type [java.util.List]");