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 (getter != null
                && (getter.returnType() == void.class
                    || getter.typeParameters().size() != 1
                    || getter.typeParameters().get(0) != int.class)) {
                throw userBraceNode.createError(
                    new IllegalArgumentException("Illegal list get shortcut for type [" + canonicalClassName + "].")
                );
            }
            if (setter != null && (setter.typeParameters().size() != 2 || setter.typeParameters().get(0) != int.class)) {
                throw userBraceNode.createError(
                    new IllegalArgumentException("Illegal list set shortcut for type [" + canonicalClassName + "].")
                );
            }
            if (getter != null
                && setter != null
                && (getter.typeParameters().get(0).equals(setter.typeParameters().get(0)) == false
                    || getter.returnType().equals(setter.typeParameters().get(1)) == false)) {
                throw userBraceNode.createError(new IllegalArgumentException("Shortcut argument types must match."));
            }
            if ((read == false || getter != null) && (write == false || setter != null)) {
                semanticScope.setCondition(userIndexNode, Read.class);
                semanticScope.putDecoration(userIndexNode, new TargetType(int.class));
                checkedVisit(userIndexNode, semanticScope);
                decorateWithCast(userIndexNode, semanticScope);
                valueType = setter != null ? setter.typeParameters().get(1) : getter.returnType();
                if (getter != null) {
                    semanticScope.putDecoration(userBraceNode, new GetterPainlessMethod(getter));
                }
                if (setter != null) {
                    semanticScope.putDecoration(userBraceNode, new SetterPainlessMethod(setter));