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
semanticScope.replicateCondition(userBlockNode, userCatchNode, AnyContinue.class);
            semanticScope.replicateCondition(userBlockNode, userCatchNode, AnyBreak.class);
        }
    }
    /**
     * Visits a throw statement.
     * Checks: type validation
     */
    @Override
    public void visitThrow(SThrow userThrowNode, SemanticScope semanticScope) {
        AExpression userExpressionNode = userThrowNode.getExpressionNode();
        semanticScope.setCondition(userExpressionNode, Read.class);
        semanticScope.putDecoration(userExpressionNode, new TargetType(Exception.class));
        checkedVisit(userExpressionNode, semanticScope);
        decorateWithCast(userExpressionNode, semanticScope);
        semanticScope.setCondition(userThrowNode, MethodEscape.class);
        semanticScope.setCondition(userThrowNode, LoopEscape.class);
        semanticScope.setCondition(userThrowNode, AllEscape.class);
    }
    /**
     * Visits a continue statement.
     * Checks: control flow
     */
    @Override
    public void visitContinue(SContinue userContinueNode, SemanticScope semanticScope) {
        if (semanticScope.getCondition(userContinueNode, InLoop.class) == false) {
            throw userContinueNode.createError(new IllegalArgumentException("invalid continue statement: not inside loop"));
        }
        if (semanticScope.getCondition(userContinueNode, LastLoop.class)) {
            throw userContinueNode.createError(new IllegalArgumentException("extraneous continue statement"));