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
new IllegalArgumentException("invalid assignment: cannot assign a value to numeric constant [" + numeric + "]")
            );
        }
        if (semanticScope.getCondition(userNumericNode, Read.class) == false) {
            throw userNumericNode.createError(new IllegalArgumentException("not a statement: numeric constant [" + numeric + "] not used"));
        }
        int radix = userNumericNode.getRadix();
        Class<?> valueType;
        Object constant;
        if (radix != 16 && (numeric.endsWith("d") || numeric.endsWith("D"))) {
            assert radix == 10;     
            try {
                constant = Double.parseDouble(numeric.substring(0, numeric.length() - 1));
                valueType = double.class;
            } catch (NumberFormatException exception) {
                throw userNumericNode.createError(new IllegalArgumentException("Invalid double constant [" + numeric + "]."));
            }
        } else if (radix != 16 && (numeric.endsWith("f") || numeric.endsWith("F"))) {
            assert radix == 10;     
            try {
                constant = Float.parseFloat(numeric.substring(0, numeric.length() - 1));
                valueType = float.class;
            } catch (NumberFormatException exception) {
                throw userNumericNode.createError(new IllegalArgumentException("Invalid float constant [" + numeric + "]."));
            }
        } else if (numeric.endsWith("l") || numeric.endsWith("L")) {
            try {
                constant = Long.parseLong(numeric.substring(0, numeric.length() - 1), radix);
                valueType = long.class;
            } catch (NumberFormatException exception) {