If a hex literal has an 'd' of 'f' in it, such as '0xf' or '0xd', the compiler fails with illegal tree structure.

The other hex literals work.  The issue is probably related to using `f` and `d` in float and double literals.

```
    public void testHexCollisionDouble() {
        assertEquals(13, exec("return 0xd"));
    }

    public void testHexCollisionFloat() {
        assertEquals(15, exec("return 0xf"));
    }

    public void testHex() throws Exception {
        for (int i = 0; i <= 15; i++) {
            String hex = Integer.toHexString(i);
            if ("d".equals(hex) || "f".equals(hex)) {
                continue;
            }
            assertEquals(i, exec("return 0x" + hex));
            assertEquals(i, exec("return 0x" + hex.toUpperCase(Locale.ROOT)));
            assertEquals(i, exec("return 0X" + hex));
            assertEquals(i, exec("return 0X" + hex.toUpperCase(Locale.ROOT)));
        }
    }
```
modules/lang-painless/src/main/java/org/elasticsearch/painless/phase/DefaultSemanticAnalysisPhase.java
}
    /**
     * Visits a list init expression which is a shortcut for initializing a list with pre-defined values.
     * Checks: type validation
     */
    @Override
    public void visitListInit(EListInit userListInitNode, SemanticScope semanticScope) {
        if (semanticScope.getCondition(userListInitNode, Write.class)) {
            throw userListInitNode.createError(
                new IllegalArgumentException("invalid assignment: cannot assign a value to list initializer")
            );
        }
        if (semanticScope.getCondition(userListInitNode, Read.class) == false) {
            throw userListInitNode.createError(new IllegalArgumentException("not a statement: result not used from list initializer"));
        }
        Class<?> valueType = ArrayList.class;
        PainlessConstructor constructor = semanticScope.getScriptScope().getPainlessLookup().lookupPainlessConstructor(valueType, 0);
        if (constructor == null) {
            throw userListInitNode.createError(
                new IllegalArgumentException("constructor [" + typeToCanonicalTypeName(valueType) + ", <init>/0] not found")
            );
        }
        semanticScope.putDecoration(userListInitNode, new StandardPainlessConstructor(constructor));
        PainlessMethod method = semanticScope.getScriptScope().getPainlessLookup().lookupPainlessMethod(valueType, false, "add", 1);
        if (method == null) {
            throw userListInitNode.createError(
                new IllegalArgumentException("method [" + typeToCanonicalTypeName(valueType) + ", add/1] not found")
            );
        }
        semanticScope.putDecoration(userListInitNode, new StandardPainlessMethod(method));