Add exceptions from frontend

exceptions/page/MDPageNotInAggregatedException.php

@@ -0,0 +1,22 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Exception thrown in case the main entity of a page (e.g. an object, an institution etc.)
+ * are not set public.
+ */
+class MDPageNotInAggregatedException extends Exception {
+
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        $errorMsg = 'There is no entity to be shown here (id: <b>' . $this->getMessage() . '</b>).';
+        return $errorMsg;
+
+    }
+
+}

exceptions/page/MDmainEntityNotPublicException.php

@@ -0,0 +1,22 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Exception thrown in case the main entity of a page (e.g. an object, an institution etc.)
+ * are not set public.
+ */
+class MDmainEntityNotPublicException extends Exception {
+
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        $errorMsg = 'There is no entity to be shown here (id: <b>' . $this->getMessage() . '</b>).';
+        return $errorMsg;
+
+    }
+
+}

exceptions/page/MDpageParameterMissingException.php

@@ -0,0 +1,21 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Custom exception class for missing page parameters.
+ */
+class MDpageParameterMissingException extends Exception {
+
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        $errorMsg = 'Parameter: <b>' . $this->getMessage() . '</b> is required but missing.';
+        return $errorMsg;
+
+    }
+
+}

exceptions/page/MDpageParameterNotNumericException.php

@@ -0,0 +1,21 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Custom exception class for invalid page parameters.
+ */
+class MDpageParameterNotNumericException extends Exception {
+
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        $errorMsg = 'Parameter: <b>' . $this->getMessage() . '</b> is not a valid, numeric values.';
+        return $errorMsg;
+
+    }
+
+}