java-native-access/jna · error · java.lang.NullPointerException

String initializer must be non-null

Error message

String initializer must be non-null

What it means

The WString constructor throws NullPointerException when given a null string. WString wraps a Java String as a wide (wchar_t*) native string, so a null initializer has no meaningful representation and JNA fails fast at construction.

Source

Thrown at src/com/sun/jna/WString.java:33

 * containing JNA, in file "LGPL2.1".
 *
 * You may obtain a copy of the Apache License at:
 *
 * http://www.apache.org/licenses/
 *
 * A copy is also included in the downloadable source code package
 * containing JNA, in file "AL2.0".
 */
package com.sun.jna;

/** Simple wrapper class to identify a wide string argument or return type.
 * @author twall@users.sf.net
 */
public final class WString implements CharSequence, Comparable {
    private String string;
    public WString(String s){
        if (s == null) {
            throw new NullPointerException("String initializer must be non-null");
        }
        this.string = s;
    }
    @Override
    public String toString() {
        return string;
    }
    @Override
    public boolean equals(Object o) {
        return (o instanceof WString) && toString().equals(o.toString());
    }
    @Override
    public int hashCode() {
        return toString().hashCode();
    }
    @Override
    public int compareTo(Object o) {
        return toString().compareTo(o.toString());

View on GitHub (pinned to d036ad9781)

Solutions

1. Check the string for null before constructing WString and substitute an empty string or skip the call.
2. If null must map to a native NULL, pass a typed null pointer (Pointer.NULL / null Pointer argument) instead of WString.
3. Fix the upstream source returning the null string.

Example fix

// before
new WString(maybeNull);
// after
if (maybeNull != null) {
    new WString(maybeNull);
} else {
    Pointer.NULL; // or handle absence explicitly
}

// Java
if (s == null) throw new IllegalArgumentException("wide string required");
WString ws = new WString(s);

WString safeWString(String s) { return (s == null) ? null : new WString(s); }

try { return new WString(s); } catch (NullPointerException e) { return null; /* or Pointer.NULL semantics */ }

When it happens

Trigger: Calling new WString(null) directly, or passing a null String through an API that converts to WString (e.g. function arguments or Native.toString-style helpers).

Common situations: Null string variables coming from configuration or native calls being wrapped as WString; missing null checks before marshalling arguments to a wide-string native function.

Related errors

• Function address may not be null
• String must not be null
• No support for " + os
• Set sun.java2d.noddraw=true to enable transparent windows
• Window must be a RootPaneContainer

AI-assisted analysis of java-native-access/jna@d036ad9781 (2026-09-12). Data as JSON: /api/errors/678617db3795347f. Report an issue: GitHub.