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
checkedVisit(userLeftNode, semanticScope);
        Class<?> leftValueType = semanticScope.getDecoration(userLeftNode, ValueType.class).valueType();
        AExpression userRightNode = userElvisNode.getRightNode();
        semanticScope.setCondition(userRightNode, Read.class);
        semanticScope.copyDecoration(userElvisNode, userRightNode, TargetType.class);
        semanticScope.replicateCondition(userElvisNode, userRightNode, Explicit.class);
        semanticScope.replicateCondition(userElvisNode, userRightNode, Internal.class);
        checkedVisit(userRightNode, semanticScope);
        Class<?> rightValueType = semanticScope.getDecoration(userRightNode, ValueType.class).valueType();
        if (userLeftNode instanceof ENull) {
            throw userElvisNode.createError(new IllegalArgumentException("Extraneous elvis operator. LHS is null."));
        }
        if (userLeftNode instanceof EBooleanConstant
            || userLeftNode instanceof ENumeric
            || userLeftNode instanceof EDecimal
            || userLeftNode instanceof EString) {
            throw userElvisNode.createError(new IllegalArgumentException("Extraneous elvis operator. LHS is a constant."));
        }
        if (leftValueType.isPrimitive()) {
            throw userElvisNode.createError(new IllegalArgumentException("Extraneous elvis operator. LHS is a primitive."));
        }
        if (userRightNode instanceof ENull) {
            throw userElvisNode.createError(new IllegalArgumentException("Extraneous elvis operator. RHS is null."));
        }
        Class<?> valueType;
        if (targetType == null) {
            Class<?> promote = AnalyzerCaster.promoteConditional(leftValueType, rightValueType);
            semanticScope.putDecoration(userLeftNode, new TargetType(promote));
            semanticScope.putDecoration(userRightNode, new TargetType(promote));
            valueType = promote;