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 (unaryType != null) {
            semanticScope.putDecoration(userUnaryNode, new UnaryType(unaryType));
        }
    }
    /**
     * Visits a binary expression which covers all the mathematical operators.
     * Checks: type validation
     */
    @Override
    public void visitBinary(EBinary userBinaryNode, SemanticScope semanticScope) {
        Operation operation = userBinaryNode.getOperation();
        if (semanticScope.getCondition(userBinaryNode, Write.class)) {
            throw userBinaryNode.createError(
                new IllegalArgumentException(
                    "invalid assignment: cannot assign a value to " + operation.name + " operation " + "[" + operation.symbol + "]"
                )
            );
        }
        if (semanticScope.getCondition(userBinaryNode, Read.class) == false) {
            throw userBinaryNode.createError(
                new IllegalArgumentException(
                    "not a statement: result not used from " + operation.name + " operation " + "[" + operation.symbol + "]"
                )
            );
        }
        AExpression userLeftNode = userBinaryNode.getLeftNode();
        semanticScope.setCondition(userLeftNode, Read.class);
        checkedVisit(userLeftNode, semanticScope);
        Class<?> leftValueType = semanticScope.getDecoration(userLeftNode, ValueType.class).valueType();
        AExpression userRightNode = userBinaryNode.getRightNode();