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 = importedMethod.typeParameters();
            valueType = importedMethod.returnType();
        } else if (classBinding != null) {
            semanticScope.putDecoration(userCallLocalNode, new StandardPainlessClassBinding(classBinding));
            semanticScope.putDecoration(userCallLocalNode, new StandardConstant(classBindingOffset));
            scriptScope.markNonDeterministic(classBinding.annotations().containsKey(NonDeterministicAnnotation.class));
            typeParameters = classBinding.typeParameters();
            valueType = classBinding.returnType();
        } else if (instanceBinding != null) {
            semanticScope.putDecoration(userCallLocalNode, new StandardPainlessInstanceBinding(instanceBinding));
            typeParameters = instanceBinding.typeParameters();
            valueType = instanceBinding.returnType();
        } else {
            throw new IllegalStateException("Illegal tree structure.");
        }
        
        
        
        for (int argument = 0; argument < userArgumentsSize; ++argument) {
            AExpression userArgumentNode = userArgumentNodes.get(argument);
            semanticScope.setCondition(userArgumentNode, Read.class);
            semanticScope.putDecoration(userArgumentNode, new TargetType(typeParameters.get(argument + classBindingOffset)));
            semanticScope.setCondition(userArgumentNode, Internal.class);
            checkedVisit(userArgumentNode, semanticScope);
            decorateWithCast(userArgumentNode, semanticScope);
        }
        semanticScope.putDecoration(userCallLocalNode, new ValueType(valueType));
    }
    /**
     * Visits a boolean constant expression.