Add asserts

src/main/kotlin/org/koitharu/kotatsu/parsers/util/Assert.kt

@@ -0,0 +1,8 @@
+package org.koitharu.kotatsu.parsers.util
+
+fun <T : Any> T?.assertNotNull(name: String): T? {
+	assert(this != null) {
+		"Value $name is null"
+	}
+	return this
+}

src/main/kotlin/org/koitharu/kotatsu/parsers/util/Parse.kt

@@ -68,10 +68,13 @@ fun String.toAbsoluteUrl(domain: String): String = when {
 }
 
 fun DateFormat.tryParse(str: String?): Long = if (str.isNullOrEmpty()) {
+	assert(false) { "Date string is null or empty" }
 	0L
 } else {
 	runCatching {
 		parse(str)?.time ?: 0L
+	}.onFailure {
+		assert(false) { "Cannot parse date $str: ${it.message}" }
 	}.getOrDefault(0L)
 }