{"record":{"id":"ff921e076b098f0f","repo":"java-native-access/jna","slug":"attempting-to-retrieve-visualid-from-a-null-visual","errorCode":null,"errorMessage":"Attempting to retrieve VisualID from a null Visual","messagePattern":"Attempting to retrieve VisualID from a null Visual","errorType":"exception","errorClass":"IllegalStateException","httpStatus":null,"severity":"error","filePath":"contrib/platform/src/com/sun/jna/platform/unix/X11.java","lineNumber":274,"sourceCode":"        private static final long serialVersionUID = 1L;\n        public static final Pixmap None = null;\n        public Pixmap() { }\n        public Pixmap(long id) { super(id); }\n        @Override\n        public Object fromNative(Object nativeValue, FromNativeContext context) {\n            if (isNone(nativeValue))\n                return None;\n            return new Pixmap(((Number)nativeValue).longValue());\n        }\n    }\n    // TODO: define structure\n    class Display extends PointerType { }\n    // TODO: define structure\n    class Visual extends PointerType {\n        public VisualID getVisualID() {\n            if (getPointer() != null)\n                return new VisualID(getPointer().getNativeLong(Native.POINTER_SIZE).longValue());\n            throw new IllegalStateException(\"Attempting to retrieve VisualID from a null Visual\");\n        }\n        @Override\n        public String toString() {\n            return \"Visual: VisualID=0x\" + Long.toHexString(getVisualID().longValue());\n        }\n    }\n    // TODO: define structure\n    class Screen extends PointerType { }\n    // TODO: define structure\n    class GC extends PointerType { }\n    // TODO: define structure\n    class XImage extends PointerType { }\n\n    /**\n     * The XQueryExtension function determines if the named extension is present.\n     * @param display Specifies the connection to the X server.\n     * @param name Specifies the extension name.\n     * @param major_opcode_return Returns the major opcode.","sourceCodeStart":256,"sourceCodeEnd":292,"githubUrl":"https://github.com/java-native-access/jna/blob/d036ad9781adad4b66693e8fa7098e4ac665e0a3/contrib/platform/src/com/sun/jna/platform/unix/X11.java#L256-L292","documentation":"X11.Visual wraps a native Xlib Visual pointer; getVisualID() reads the VisualID field at offset POINTER_SIZE. If the underlying pointer is null there is no native Visual to read, so an IllegalStateException is thrown. toString() calls getVisualID(), so even printing a null Visual triggers it.","triggerScenarios":"Calling toString() (or getVisualID()) on a Visual object constructed without a valid native pointer, e.g. Visual obtained from an API that returned NULL or a default-constructed Visual.","commonSituations":"Debug/logging code that stringifies Visual objects received from XGetVisualInfo or window attributes where the visual pointer was NULL; uninitialized Visual instances.","solutions":["Check getPointer() != null before calling getVisualID() or toString()","Ensure the Visual was obtained from a successful X11 call and not a NULL return","Catch IllegalStateException in logging paths and print a placeholder"],"exampleFix":"// before\nSystem.out.println(\"visual=\" + visual);\n// after\nSystem.out.println(\"visual=\" + (visual.getPointer() != null ? visual : \"<null visual>\"));","handlingStrategy":"type-guard","validationCode":"if (visual == null || visual.getPointer() == null) {\n    return; // no native Visual to inspect\n}","typeGuard":"boolean hasNativeVisual(X11.Visual v) { return v != null && v.getPointer() != null; }","tryCatchPattern":"try { id = visual.getVisualID(); } catch (IllegalStateException e) { id = null; }","preventionTips":["Only construct Visual from non-NULL pointers returned by Xlib calls","Null-check getPointer() before toString()/getVisualID()","Avoid stringifying Visual objects in log statements without guarding"],"tags":["x11","unix","null-pointer","visual"],"backgroundTag":"null-argument","analyzedSha":"d036ad9781adad4b66693e8fa7098e4ac665e0a3","analyzedAt":"2026-09-12T06:50:59.239Z","contentChangedAt":"2026-09-12T06:50:59.239Z","schemaVersion":2},"datasetVersion":"2026-09-14T05:17:10.506Z"}