Fixed nullability

The convertValue method can accept null, but was defined as non-null.

Author: k163377

src/main/kotlin/com/fasterxml/jackson/module/kotlin/Extensions.kt

@@ -61,7 +61,7 @@ inline fun <reified T> ObjectMapper.readValue(src: InputStream): T = readValue(s
 inline fun <reified T> ObjectMapper.readValue(src: ByteArray): T = readValue(src, jacksonTypeRef<T>())
 
 inline fun <reified T> ObjectMapper.treeToValue(n: TreeNode): T = readValue(this.treeAsTokens(n), jacksonTypeRef<T>())
-inline fun <reified T> ObjectMapper.convertValue(from: Any): T = convertValue(from, jacksonTypeRef<T>())
+inline fun <reified T> ObjectMapper.convertValue(from: Any?): T = convertValue(from, jacksonTypeRef<T>())
 
 inline fun <reified T> ObjectReader.readValueTyped(jp: JsonParser): T = readValue(jp, jacksonTypeRef<T>())
 inline fun <reified T> ObjectReader.readValuesTyped(jp: JsonParser): Iterator<T> = readValues(jp, jacksonTypeRef<T>())