Error map

Undefined array key Warning: Undefined array key / Undefined index

PHP · layer 4, Application & API

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Centre: this error. First ring: errors it is linked with (7). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.

1 · On your device 2 · Network 4 · Application & API 6 · Platform & cloud
Undefined array key — Warning: Undefined array key / Undefined index (PHP)Undefined a…TypeError — TypeError: Cannot read properties of undefined (reading 'x') (JavaScript)TypeErrorreduce empty — TypeError: Reduce of empty array with no initial value (JavaScript)reduce emptyArrayIndexOutOfBoundsException — java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5 (Java)ArrayIndexOutOfBoun…Headers already sent — Warning: Cannot modify header information - headers already sent (PHP)Headers already sentArray offset on null — Warning: Trying to access array offset on value of type null (PHP)Array offset on nullKeyError — KeyError: 'x' (Python)KeyErrorinvalid array length — RangeError: Invalid array length (JavaScript)invalid array lengthNullReferenceException — System.NullReferenceException: Object reference not set to an instance of an object (.NET)NullReferenceExcept…TypeError: not a function — TypeError: x is not a function (JavaScript)TypeError: not a fu…ReferenceError — ReferenceError: x is not defined (JavaScript)ReferenceErrorAbortError — AbortError: The user aborted a request. / signal is aborted without reason (JavaScript)AbortErrorbody already used — TypeError: Failed to execute 'json' on 'Response': body stream already read (JavaScript)body already usedreading length — TypeError: Cannot read properties of undefined (reading 'length') (JavaScript)reading lengthStringIndexOutOfBoundsException — java.lang.StringIndexOutOfBoundsException: begin 0, end 10, length 5 (Java)StringIndexOutOfBou…UnsupportedOperationException — java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable) (Java)UnsupportedOperatio…Stream closed — java.io.IOException: Stream closed (Java)Stream closed500 — HTTP 500 Internal Server Error (HTTP)500Call to undefined function — PHP Fatal error: Uncaught Error: Call to undefined function (PHP)Call to undefined f…Not a valid JSON response — WordPress: Updating failed. The response is not a valid JSON response. (WordPress)Not a valid JSON re…TypeError not iterable — TypeError: x is not iterable (JavaScript)TypeError not itera…Object.keys null — TypeError: Cannot convert undefined or null to object (JavaScript)Object.keys nullUndefined variable — Warning: Undefined variable $x (PHP)Undefined variableTypeError: NoneType — TypeError: 'NoneType' object is not subscriptable (Python)TypeError: NoneTypeAttributeError — AttributeError: 'X' object has no attribute 'y' (Python)AttributeErrorCreateContainerConfigError — Kubernetes: CreateContainerConfigError — secret / configmap not found (Kubernetes)CreateContainerConf…Aw, Snap! — Chrome: Aw, Snap! Something went wrong while displaying this webpage. Error code: STATUS_ACCESS_VIOLATION / SIGILL / Out of Memory (Browser)Aw, Snap!

Directly related (7)

TypeErrorJavaScript

TypeError: Cannot read properties of undefined (reading 'x')

You tried to access a property on a value that is `undefined` (or `null`) — usually data that hasn’t loaded yet or a wrong proper…

reduce emptyJavaScript

TypeError: Reduce of empty array with no initial value

Array.reduce() ran on an empty array without an initial value.

ArrayIndexOutOfBoundsExceptionJava

java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5

Code accessed an array index outside 0 … length-1.

Headers already sentPHP

Warning: Cannot modify header information - headers already sent

You called `header()`, `setcookie()` or `session_start()` after output had already been sent to the browser.

Array offset on nullPHP

Warning: Trying to access array offset on value of type null

Code used `$x['key']` where `$x` is null — usually a lookup or function that returned nothing.

KeyErrorPython

KeyError: 'x'

You accessed a dictionary key that doesn’t exist.

invalid array lengthJavaScript

RangeError: Invalid array length

An array was created or resized with a negative, fractional or enormous length.

Two steps away (19)

NullReferenceException.NET

System.NullReferenceException: Object reference not set to an instance of an object

Code dereferenced a variable that is `null` — the .NET equivalent of Java’s NullPointerException.

TypeError: not a functionJavaScript

TypeError: x is not a function

You called something as a function, but its value is not a function (it’s undefined, a string, an object…).

ReferenceErrorJavaScript

ReferenceError: x is not defined

Code refers to a variable or function name that doesn’t exist in the current scope.

AbortErrorJavaScript

AbortError: The user aborted a request. / signal is aborted without reason

A fetch was cancelled through an AbortController (or the browser cancelled it).

body already usedJavaScript

TypeError: Failed to execute 'json' on 'Response': body stream already read

A fetch Response body was consumed twice (e.g. calling .text() then .json()).

reading lengthJavaScript

TypeError: Cannot read properties of undefined (reading 'length')

Code checked .length on something that is undefined — typically an array or string that hasn’t loaded.

StringIndexOutOfBoundsExceptionJava

java.lang.StringIndexOutOfBoundsException: begin 0, end 10, length 5

substring()/charAt() used an index outside the string.

UnsupportedOperationExceptionJava

java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable)

Code tried to modify an immutable or fixed-size collection.

Stream closedJava

java.io.IOException: Stream closed

Code read or wrote a stream after it was closed — often by a try-with-resources block or a wrapper closing the underlying stream.

500HTTP

HTTP 500 Internal Server Error

The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.

Call to undefined functionPHP

PHP Fatal error: Uncaught Error: Call to undefined function

PHP can’t find the function you called — usually a missing extension, missing include, or namespace issue.

Not a valid JSON responseWordPress

WordPress: Updating failed. The response is not a valid JSON response.

The block editor saved via the REST API but got HTML or an error page back — broken permalinks, a security plugin/WAF, or PHP out…

TypeError not iterableJavaScript

TypeError: x is not iterable

for…of, spread or destructuring was used on something that isn’t an array/iterable.

Object.keys nullJavaScript

TypeError: Cannot convert undefined or null to object

Object.keys/entries/assign was called with undefined or null.

Undefined variablePHP

Warning: Undefined variable $x

PHP read a variable that was never assigned in the current scope.

TypeError: NoneTypePython

TypeError: 'NoneType' object is not subscriptable

You used `[ ]` on a value that is `None` — typically a function that returned nothing.

AttributeErrorPython

AttributeError: 'X' object has no attribute 'y'

You accessed an attribute or method that doesn’t exist on that object type.

CreateContainerConfigErrorKubernetes

Kubernetes: CreateContainerConfigError — secret / configmap not found

Kubernetes can’t build the container’s configuration — usually a referenced Secret, ConfigMap or key doesn’t exist in that namesp…

Aw, Snap!Browser

Chrome: Aw, Snap! Something went wrong while displaying this webpage. Error code: STATUS_ACCESS_VIOLATION / SIGILL / Out of Memory

A Chrome tab crashed — out of memory, a faulty extension, a graphics/driver issue or a very heavy page.

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