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
* Visits a try statement.
     * Checks: control flow
     */
    @Override
    public void visitTry(STry userTryNode, SemanticScope semanticScope) {
        SBlock userBlockNode = userTryNode.getBlockNode();
        if (userBlockNode == null) {
            throw userTryNode.createError(new IllegalArgumentException("extraneous try statement"));
        }
        semanticScope.replicateCondition(userTryNode, userBlockNode, LastSource.class);
        semanticScope.replicateCondition(userTryNode, userBlockNode, InLoop.class);
        semanticScope.replicateCondition(userTryNode, userBlockNode, LastLoop.class);
        visit(userBlockNode, semanticScope.newLocalScope());
        boolean methodEscape = semanticScope.getCondition(userBlockNode, MethodEscape.class);
        boolean loopEscape = semanticScope.getCondition(userBlockNode, LoopEscape.class);
        boolean allEscape = semanticScope.getCondition(userBlockNode, AllEscape.class);
        boolean anyContinue = semanticScope.getCondition(userBlockNode, AnyContinue.class);
        boolean anyBreak = semanticScope.getCondition(userBlockNode, AnyBreak.class);
        for (SCatch userCatchNode : userTryNode.getCatchNodes()) {
            semanticScope.replicateCondition(userTryNode, userCatchNode, LastSource.class);
            semanticScope.replicateCondition(userTryNode, userCatchNode, InLoop.class);
            semanticScope.replicateCondition(userTryNode, userCatchNode, LastLoop.class);
            visit(userCatchNode, semanticScope.newLocalScope());
            methodEscape &= semanticScope.getCondition(userCatchNode, MethodEscape.class);
            loopEscape &= semanticScope.getCondition(userCatchNode, LoopEscape.class);
            allEscape &= semanticScope.getCondition(userCatchNode, AllEscape.class);
            anyContinue |= semanticScope.getCondition(userCatchNode, AnyContinue.class);
            anyBreak |= semanticScope.getCondition(userCatchNode, AnyBreak.class);
        }
        if (methodEscape) {