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
}
            if (staticType != null) {
                if (write) {
                    throw userDotNode.createError(
                        new IllegalArgumentException(
                            "invalid assignment: "
                                + "cannot write a value to a static type ["
                                + PainlessLookupUtility.typeToCanonicalTypeName(staticType)
                                + "]"
                        )
                    );
                }
                semanticScope.putDecoration(userDotNode, new StaticType(staticType));
            } else {
                Class<?> valueType = null;
                if (prefixValueType != null && prefixValueType.valueType().isArray()) {
                    if ("length".equals(index)) {
                        if (write) {
                            throw userDotNode.createError(
                                new IllegalArgumentException(
                                    "invalid assignment: cannot assign a value write to read-only field [length] for an array."
                                )
                            );
                        }
                        valueType = int.class;
                    } else {
                        throw userDotNode.createError(
                            new IllegalArgumentException(
                                "Field [" + index + "] does not exist for type [" + prefixValueType.getValueCanonicalTypeName() + "]."
                            )