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/main/java/org/elasticsearch/painless/phase/DefaultSemanticAnalysisPhase.java
}
                                semanticScope.setCondition(userDotNode, MapShortcut.class);
                            }
                            if (List.class.isAssignableFrom(prefixType)) {
                                try {
                                    scriptScope.putDecoration(userDotNode, new StandardConstant(Integer.parseInt(index)));
                                } catch (NumberFormatException nfe) {
                                    throw userDotNode.createError(new IllegalArgumentException("invalid list index [" + index + "]", nfe));
                                }
                                getter = scriptScope.getPainlessLookup().lookupPainlessMethod(prefixType, false, "get", 1);
                                setter = scriptScope.getPainlessLookup().lookupPainlessMethod(prefixType, false, "set", 2);
                                if (getter != null
                                    && (getter.returnType() == void.class
                                        || getter.typeParameters().size() != 1
                                        || getter.typeParameters().get(0) != int.class)) {
                                    throw userDotNode.createError(
                                        new IllegalArgumentException(
                                            "Illegal list get shortcut for type [" + prefixCanonicalTypeName + "]."
                                        )
                                    );
                                }
                                if (setter != null
                                    && (setter.typeParameters().size() != 2 || setter.typeParameters().get(0) != int.class)) {
                                    throw userDotNode.createError(
                                        new IllegalArgumentException(
                                            "Illegal list set shortcut for type [" + prefixCanonicalTypeName + "]."
                                        )
                                    );
                                }
                                if (getter != null