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
import org.elasticsearch.painless.node.ECall;
import org.elasticsearch.painless.node.ECallLocal;
import org.elasticsearch.painless.node.EComp;
import org.elasticsearch.painless.node.EConditional;
import org.elasticsearch.painless.node.EDecimal;
import org.elasticsearch.painless.node.EDot;
import org.elasticsearch.painless.node.EElvis;
import org.elasticsearch.painless.node.EExplicit;
import org.elasticsearch.painless.node.EFunctionRef;
import org.elasticsearch.painless.node.EInstanceof;
import org.elasticsearch.painless.node.ELambda;
import org.elasticsearch.painless.node.EListInit;
import org.elasticsearch.painless.node.EMapInit;
import org.elasticsearch.painless.node.ENewArray;
import org.elasticsearch.painless.node.ENewArrayFunctionRef;
import org.elasticsearch.painless.node.ENewObj;
import org.elasticsearch.painless.node.ENull;
import org.elasticsearch.painless.node.ENumeric;
import org.elasticsearch.painless.node.ERegex;
import org.elasticsearch.painless.node.EString;
import org.elasticsearch.painless.node.ESymbol;
import org.elasticsearch.painless.node.EUnary;
import org.elasticsearch.painless.node.SBlock;
import org.elasticsearch.painless.node.SBreak;
import org.elasticsearch.painless.node.SCatch;
import org.elasticsearch.painless.node.SClass;
import org.elasticsearch.painless.node.SContinue;
import org.elasticsearch.painless.node.SDeclBlock;
import org.elasticsearch.painless.node.SDeclaration;
import org.elasticsearch.painless.node.SDo;