JSON response string ends with "null" - php

Question

In both Postman and jQuery, I'm getting responses in the form
{"key1": "value1", "key2": "value2"}null
That trailing null is messing with anything that tries to parse it client-side and I can't figure out where it's coming from. If I error_log the encoded JSON before echoing it, there's no trailing null, so I assume that it's a string terminator, but I didn't think that PHP used null-terminated strings. How do I get rid of these nulls?
The object being encoded and returned:
public function jsonSerialize()
{
return [
'internal_id' => $this->internal_id, //int
'friendly_name' => $this->friendly_name, //string
'external_id' => $this->external_id, //string
'picture' => $this->picture //string
];
}
The actual return statement is just echo(json_encode($retval));

Answer 1

Once a PHP file has executed, you have to exit manually or return instead of echoing, otherwise it'll return NULL implicitly and mess everything up. Lesson learned.

Answer 2

Not the most elegant probably... but this SAVED me:
function removeTrailingNulls(__str){
var sanitized = __str;
var lastCharIndex = sanitized.length - 1;
var lastChar = sanitized[lastCharIndex];
var lastCharCode = lastChar.charCodeAt(0);
var isWeirdNullSpace = lastCharCode === 0;
console.log('checking last char (' + lastChar + ') code: ' + lastCharCode + '...null space end?' + isWeirdNullSpace);
var loopCount = 0;
while(isWeirdNullSpace){
sanitized = sanitized.substring(0, sanitized.length-1);
lastChar = sanitized[sanitized.length-1];
lastCharCode = lastChar.charCodeAt(0);
isWeirdNullSpace = lastCharCode === 0;
loopCount++;
if(loopCount>100) break; // prevent infinite loops just in case.
}
return String(sanitized);
}