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
boolean dynamic = false;
        PainlessMethod method = null;
        if (prefixValueType != null) {
            Class<?> type = prefixValueType.valueType();
            PainlessLookup lookup = semanticScope.getScriptScope().getPainlessLookup();
            if (prefixValueType.valueType() == def.class) {
                dynamic = true;
            } else {
                method = lookup.lookupPainlessMethod(type, false, methodName, userArgumentsSize);
                if (method == null) {
                    dynamic = lookup.lookupPainlessClass(type).annotations.containsKey(DynamicTypeAnnotation.class)
                        && lookup.lookupPainlessSubClassesMethod(type, methodName, userArgumentsSize) != null;
                    if (dynamic == false) {
                        throw userCallNode.createError(
                            new IllegalArgumentException(
                                "member method "
                                    + "["
                                    + prefixValueType.getValueCanonicalTypeName()
                                    + ", "
                                    + methodName
                                    + "/"
                                    + userArgumentsSize
                                    + "] "
                                    + "not found"
                            )
                        );
                    }
                }
            }
        } else if (prefixStaticType != null) {