Ensure types safety and return an empty string when the header field doesn't exist

Author: na2axl

src/WaterPipe/HTTP/Header.php

@@ -51,7 +51,7 @@ public function setField(string $name, string $value)
 
     public function getField(string $name): string
     {
-        return $this->_fields[$name];
+        return array_key_exists($name, $this->_fields) ? $this->_fields[$name] : "";
     }
 
     public function toArray(): array

src/WaterPipe/HTTP/Request/RequestHeader.php

@@ -138,12 +138,12 @@ public function getConnection(): string
 
     public function setContentLength(int $value)
     {
-        $this->setField("Content-Length", $value);
+        $this->setField("Content-Length", strval($value));
     }
 
     public function getContentLength(): int
     {
-        return $this->getField("Content-Length");
+        return intval($this->getField("Content-Length"));
     }
 
     public function setContentType(string $value)
@@ -258,12 +258,12 @@ public function getIfUnmodifiedSince(): string
 
     public function setMaxForward(int $value)
     {
-        $this->setField("Max-Forward", $value);
+        $this->setField("Max-Forward", strval($value));
     }
 
     public function getMaxForward(): int
     {
-        return $this->getField("Max-Forward");
+        return intval($this->getField("Max-Forward"));
     }
 
     public function setOrigin(string $value)

src/WaterPipe/HTTP/Response/ResponseHeader.php

@@ -68,12 +68,12 @@ public function getAcceptRanges(): string
 
     public function setAge(int $value)
     {
-        $this->setField("Age", $value);
+        $this->setField("Age", strval($value));
     }
 
     public function getAge(): int
     {
-        return $this->getField("Age");
+        return intval($this->getField("Age"));
     }
 
     public function setAllow(string $value)
@@ -148,12 +148,12 @@ public function getContentLanguage(): string
 
     public function setContentLength(int $value)
     {
-        $this->setField("Content-Length", $value);
+        $this->setField("Content-Length", strval($value));
     }
 
     public function getContentLength(): int
     {
-        return $this->getField("Content-Length");
+        return intval($this->getField("Content-Length"));
     }
 
     public function setContentLocation(string $value)