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
+ typeParameters.size()
                        + "] parameters"
                )
            );
        }
        functionScope.setCondition(userBlockNode, LastSource.class);
        visit(userBlockNode, functionScope.newLocalScope());
        boolean methodEscape = functionScope.getCondition(userBlockNode, MethodEscape.class);
        boolean isAutoReturnEnabled = userFunctionNode.isAutoReturnEnabled();
        if (methodEscape == false && isAutoReturnEnabled == false && returnType != void.class) {
            throw userFunctionNode.createError(
                new IllegalArgumentException(
                    "invalid function definition: "
                        + "not all paths provide a return value for function "
                        + "["
                        + functionName
                        + "] with ["
                        + typeParameters.size()
                        + "] parameters"
                )
            );
        }
        if (methodEscape) {
            functionScope.setCondition(userFunctionNode, MethodEscape.class);
        }
    }
    /**
     * Visits a block and which contains one-to-many statements.
     * Checks: control flow
     */