Description:
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The same code snippet (see below) works properly in Ubuntu 14.04, which has Imagick 6.7 installed in it.

Test script:
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$plateWidth = 142;
$plateHeight = 40;
$platePositionX = 434;
$platePositionY = 171;
$fontColor = '#43B19C';
$transparentColor = '#00000000';
$fontPath = 'PUT HERE VALID PATH TO YOUR FONT FILE';

$text = '';

$plate = new Imagick();
$plate->newImage($plateWidth, $plateHeight, new ImagickPixel($transparentColor));
$plate->setBackgroundColor(new ImagickPixel($transparentColor));
$plate->setFont($fontPath);
$plate->setGravity(Imagick::GRAVITY_CENTER);
$plate->newPseudoImage($plateWidth, $plateHeight, "caption:{$text}");

Expected result:
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The empty plate image is rendered.
If the format "caption:" with empty text is not allowed, a clear error message should be shown to the user (developer).

Actual result:
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The php-fpm/apache process hangs, takes longer than 30+2 seconds and eventually crashes because of execution timeout.