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
);
        }
        AExpression userPrefixNode = userCallNode.getPrefixNode();
        semanticScope.setCondition(userPrefixNode, Read.class);
        visit(userPrefixNode, semanticScope);
        ValueType prefixValueType = semanticScope.getDecoration(userPrefixNode, ValueType.class);
        StaticType prefixStaticType = semanticScope.getDecoration(userPrefixNode, StaticType.class);
        if (prefixValueType != null && prefixStaticType != null) {
            throw userCallNode.createError(
                new IllegalStateException(
                    "cannot have both "
                        + "value ["
                        + prefixValueType.getValueCanonicalTypeName()
                        + "] "
                        + "and type ["
                        + prefixStaticType.getStaticCanonicalTypeName()
                        + "]"
                )
            );
        }
        if (semanticScope.hasDecoration(userPrefixNode, PartialCanonicalTypeName.class)) {
            throw userCallNode.createError(
                new IllegalArgumentException(
                    "cannot resolve symbol "
                        + "["
                        + semanticScope.getDecoration(userPrefixNode, PartialCanonicalTypeName.class).partialCanonicalTypeName()
                        + "]"
                )
            );
        }