Merge branch '5.1' into master

* 5.1:
  fix merge
  [Cache] fix previous PR
  add mising sr (latn & cyrl) translations
  [Cache] fix ProxyAdapter not persisting items with infinite expiration
  [HttpClient] fail properly when the server replies with HTTP/0.9
  Fix CS
  [Cache] Limit cache version character range
  [Mailer] Fixed Mailgun API bridge JsonException when API response is not applicaton/json
  [String] improve fix
  fix tests
  [DI] dump OS-indepent paths in the compiled container
  [DI] dump OS-indepent paths in the preload file
  Run postgres setup trigger in transaction
  allow consumers to mock all methods

UnicodeString.php

@@ -143,12 +143,12 @@ public function indexOf($needle, int $offset = 0): ?int
             return null;
         }
 
-        if ($this->length() <= $offset) {
+        try {
+            $i = $this->ignoreCase ? grapheme_stripos($this->string, $needle, $offset) : grapheme_strpos($this->string, $needle, $offset);
+        } catch (\ValueError $e) {
             return null;
         }
 
-        $i = $this->ignoreCase ? grapheme_stripos($this->string, $needle, $offset) : grapheme_strpos($this->string, $needle, $offset);
-
         return false === $i ? null : $i;
     }
 
@@ -266,12 +266,12 @@ public function replaceMatches(string $fromRegexp, $to): AbstractString
 
     public function slice(int $start = 0, int $length = null): AbstractString
     {
-        if ($this->length() <= $start) {
-            return new self();
-        }
-
         $str = clone $this;
-        $str->string = (string) grapheme_substr($this->string, $start, $length ?? \PHP_INT_MAX);
+        try {
+            $str->string = (string) grapheme_substr($this->string, $start, $length ?? \PHP_INT_MAX);
+        } catch (\ValueError $e) {
+            $str->string = '';
+        }
 
         return $str;
     }