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
PainlessMethod setter;
                        getter = scriptScope.getPainlessLookup()
                            .lookupPainlessMethod(
                                prefixType,
                                isStatic,
                                "get" + Character.toUpperCase(index.charAt(0)) + index.substring(1),
                                0
                            );
                        if (getter == null) {
                            getter = scriptScope.getPainlessLookup()
                                .lookupPainlessMethod(
                                    prefixType,
                                    isStatic,
                                    "is" + Character.toUpperCase(index.charAt(0)) + index.substring(1),
                                    0
                                );
                        }
                        setter = scriptScope.getPainlessLookup()
                            .lookupPainlessMethod(
                                prefixType,
                                isStatic,
                                "set" + Character.toUpperCase(index.charAt(0)) + index.substring(1),
                                1
                            );
                        if (getter != null || setter != null) {
                            if (getter != null && (getter.returnType() == void.class || getter.typeParameters().isEmpty() == false)) {
                                throw userDotNode.createError(
                                    new IllegalArgumentException(
                                        "Illegal get shortcut on field [" + index + "] for type [" + prefixCanonicalTypeName + "]."
                                    )