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 (classBinding == null) {
                            instanceBinding = scriptScope.getPainlessLookup().lookupPainlessInstanceBinding(methodName, userArgumentsSize);
                            if (instanceBinding == null) {
                                throw userCallLocalNode.createError(
                                    new IllegalArgumentException(
                                        "Unknown call [" + methodName + "] with [" + userArgumentsSize + "] arguments."
                                    )
                                );
                            }
                        }
                    }
                }
            }
        }
        List<Class<?>> typeParameters;
        if (localFunction != null) {
            semanticScope.setUsesInstanceMethod();
            semanticScope.putDecoration(userCallLocalNode, new StandardLocalFunction(localFunction));
            typeParameters = localFunction.getTypeParameters();
            valueType = localFunction.getReturnType();
        } else if (thisMethod != null) {
            semanticScope.setUsesInstanceMethod();
            semanticScope.putDecoration(userCallLocalNode, new ThisPainlessMethod(thisMethod));
            scriptScope.markNonDeterministic(thisMethod.annotations().containsKey(NonDeterministicAnnotation.class));
            typeParameters = thisMethod.typeParameters();
            valueType = thisMethod.returnType();
        } else if (importedMethod != null) {
            semanticScope.putDecoration(userCallLocalNode, new StandardPainlessMethod(importedMethod));
            scriptScope.markNonDeterministic(importedMethod.annotations().containsKey(NonDeterministicAnnotation.class));