diff --git a/gst/gstallocator.c b/gst/gstallocator.c
index c4b21b3efc..a6e6039def 100644
--- a/gst/gstallocator.c
+++ b/gst/gstallocator.c
@@ -218,7 +218,7 @@ gst_allocator_register (const gchar * name, GstAllocator * allocator)
 
 /**
  * gst_allocator_find:
- * @name: the name of the allocator
+ * @name: (allow-none): the name of the allocator
  *
  * Find a previously registered allocator with @name. When @name is NULL, the
  * default allocator will be returned.
diff --git a/gst/gstevent.c b/gst/gstevent.c
index 4693c35d65..0874471986 100644
--- a/gst/gstevent.c
+++ b/gst/gstevent.c
@@ -1610,8 +1610,8 @@ gst_event_new_segment_done (GstFormat format, gint64 position)
 /**
  * gst_event_parse_segment_done:
  * @event: A valid #GstEvent of type GST_EVENT_SEGMENT_DONE.
- * @format: (out): Result location for the format, or NULL
- * @position: (out): Result location for the position, or NULL
+ * @format: (out) (allow-none): Result location for the format, or NULL
+ * @position: (out) (allow-none): Result location for the position, or NULL
  *
  * Extracts the position and format from the segment done message.
  *
diff --git a/gst/gstghostpad.c b/gst/gstghostpad.c
index 4f98bffda8..98712d8aa6 100644
--- a/gst/gstghostpad.c
+++ b/gst/gstghostpad.c
@@ -77,7 +77,7 @@ static GstPad *gst_proxy_pad_get_target (GstPad * pad);
 /**
  * gst_proxy_pad_iterate_internal_links_default:
  * @pad: the #GstPad to get the internal links of.
- * @parent: the parent of @pad or NULL
+ * @parent: (allow-none): the parent of @pad or NULL
  *
  * Invoke the default iterate internal links function of the proxy pad.
  *
@@ -106,7 +106,7 @@ gst_proxy_pad_iterate_internal_links_default (GstPad * pad, GstObject * parent)
 /**
  * gst_proxy_pad_chain_default:
  * @pad: a sink #GstPad, returns GST_FLOW_ERROR if not.
- * @parent: the parent of @pad or NULL
+ * @parent: (allow-none): the parent of @pad or NULL
  * @buffer: (transfer full): the #GstBuffer to send, return GST_FLOW_ERROR
  *     if not.
  *
@@ -134,7 +134,7 @@ gst_proxy_pad_chain_default (GstPad * pad, GstObject * parent,
 /**
  * gst_proxy_pad_chain_list_default:
  * @pad: a sink #GstPad, returns GST_FLOW_ERROR if not.
- * @parent: the parent of @pad or NULL
+ * @parent: (allow-none): the parent of @pad or NULL
  * @list: (transfer full): the #GstBufferList to send, return GST_FLOW_ERROR
  *     if not.
  *
@@ -334,7 +334,7 @@ gst_ghost_pad_internal_activate_pull_default (GstPad * pad, GstObject * parent,
 /**
  * gst_ghost_pad_internal_activate_mode_default:
  * @pad: the #GstPad to activate or deactivate.
- * @parent: the parent of @pad or NULL
+ * @parent: (allow-none): the parent of @pad or NULL
  * @mode: the requested activation mode
  * @active: whether the pad should be active or not.
  *
@@ -422,7 +422,7 @@ gst_ghost_pad_activate_pull_default (GstPad * pad, GstObject * parent,
 /**
  * gst_ghost_pad_activate_mode_default:
  * @pad: the #GstPad to activate or deactivate.
- * @parent: the parent of @pad or NULL
+ * @parent: (allow-none): the parent of @pad or NULL
  * @mode: the requested activation mode
  * @active: whether the pad should be active or not.
  *
diff --git a/gst/gstinfo.h b/gst/gstinfo.h
index 7f297af27c..68f099b5ae 100644
--- a/gst/gstinfo.h
+++ b/gst/gstinfo.h
@@ -494,7 +494,7 @@ GST_EXPORT GstDebugLevel            _gst_debug_min;
  * GST_CAT_LEVEL_LOG:
  * @cat: category to use
  * @level: the severity of the message
- * @object: the #GObject the message belongs to or NULL if none
+ * @object: (allow-none): the #GObject the message belongs to or NULL if none
  * @...: A printf-style message to output
  *
  * Outputs a debugging message. This is the most general macro for outputting
diff --git a/gst/gstmessage.c b/gst/gstmessage.c
index 2b231c4883..cb81bf7e7f 100644
--- a/gst/gstmessage.c
+++ b/gst/gstmessage.c
@@ -1372,8 +1372,8 @@ gst_message_parse_info (GstMessage * message, GError ** gerror, gchar ** debug)
 /**
  * gst_message_parse_segment_start:
  * @message: A valid #GstMessage of type GST_MESSAGE_SEGMENT_START.
- * @format: (out): Result location for the format, or NULL
- * @position: (out): Result location for the position, or NULL
+ * @format: (out) (allow-none): Result location for the format, or NULL
+ * @position: (out) (allow-none): Result location for the position, or NULL
  *
  * Extracts the position and format from the segment start message.
  *
@@ -1402,8 +1402,8 @@ gst_message_parse_segment_start (GstMessage * message, GstFormat * format,
 /**
  * gst_message_parse_segment_done:
  * @message: A valid #GstMessage of type GST_MESSAGE_SEGMENT_DONE.
- * @format: (out): Result location for the format, or NULL
- * @position: (out): Result location for the position, or NULL
+ * @format: (out) (allow-none): Result location for the format, or NULL
+ * @position: (out) (allow-none): Result location for the position, or NULL
  *
  * Extracts the position and format from the segment done message.
  *
@@ -1432,7 +1432,7 @@ gst_message_parse_segment_done (GstMessage * message, GstFormat * format,
 /**
  * gst_message_parse_async_done:
  * @message: A valid #GstMessage of type GST_MESSAGE_ASYNC_DONE.
- * @running_time: (out): Result location for the running_time or NULL
+ * @running_time: (out) (allow-none): Result location for the running_time or NULL
  *
  * Extract the running_time from the async_done message.
  *
@@ -1456,7 +1456,7 @@ gst_message_parse_async_done (GstMessage * message, GstClockTime * running_time)
 /**
  * gst_message_parse_request_state:
  * @message: A valid #GstMessage of type GST_MESSAGE_REQUEST_STATE.
- * @state: (out): Result location for the requested state or NULL
+ * @state: (out) (allow-none): Result location for the requested state or NULL
  *
  * Extract the requested state from the request_state message.
  *
@@ -2108,7 +2108,8 @@ gst_message_new_reset_time (GstObject * src, GstClockTime running_time)
 /**
  * gst_message_parse_reset_time:
  * @message: A valid #GstMessage of type GST_MESSAGE_RESET_TIME.
- * @running_time: (out): Result location for the running_time or NULL
+ * @running_time: (out) (allow-none): Result location for the running_time or
+ *      NULL
  *
  * Extract the running-time from the RESET_TIME message.
  *
@@ -2315,7 +2316,8 @@ gst_message_new_have_context (GstObject * src, GstContext * context)
 /**
  * gst_message_parse_have_context:
  * @message: A valid #GstMessage of type GST_MESSAGE_HAVE_CONTEXT.
- * @context: (out) (transfer full): Result location for the context or NULL
+ * @context: (out) (transfer full) (allow-none): Result location for the
+ *      context or NULL
  *
  * Extract the context from the HAVE_CONTEXT message.
  *
diff --git a/gst/gstminiobject.c b/gst/gstminiobject.c
index 8b21709a77..25efc084b6 100644
--- a/gst/gstminiobject.c
+++ b/gst/gstminiobject.c
@@ -106,9 +106,9 @@ _priv_gst_mini_object_initialize (void)
  * @mini_object: a #GstMiniObject
  * @flags: initial #GstMiniObjectFlags
  * @type: the #GType of the mini-object to create
- * @copy_func: the copy function, or NULL
- * @dispose_func: the dispose function, or NULL
- * @free_func: the free function or NULL
+ * @copy_func: (allow-none): the copy function, or NULL
+ * @dispose_func: (allow-none): the dispose function, or NULL
+ * @free_func: (allow-none): the free function or NULL
  *
  * Initializes a mini-object with the desired type and copy/dispose/free
  * functions.
diff --git a/gst/gstpad.c b/gst/gstpad.c
index 138ed2eb52..e1f386a127 100644
--- a/gst/gstpad.c
+++ b/gst/gstpad.c
@@ -2544,7 +2544,7 @@ no_peer:
 /**
  * gst_pad_iterate_internal_links_default:
  * @pad: the #GstPad to get the internal links of.
- * @parent: the parent of @pad or NULL
+ * @parent: (allow-none): the parent of @pad or NULL
  *
  * Iterate the list of pads to which the given pad is linked to inside of
  * the parent element.
@@ -2753,7 +2753,7 @@ event_forward_func (GstPad * pad, EventData * data)
 /**
  * gst_pad_event_default:
  * @pad: a #GstPad to call the default event handler on.
- * @parent: the parent of @pad or NULL
+ * @parent: (allow-none): the parent of @pad or NULL
  * @event: (transfer full): the #GstEvent to handle.
  *
  * Invokes the default event handler for the given pad.
@@ -2943,7 +2943,7 @@ query_forward_func (GstPad * pad, QueryData * data)
 /**
  * gst_pad_query_default:
  * @pad: a #GstPad to call the default query handler on.
- * @parent: the parent of @pad or NULL
+ * @parent: (allow-none): the parent of @pad or NULL
  * @query: (transfer none): the #GstQuery to handle.
  *
  * Invokes the default query handler for the given pad.
diff --git a/gst/gstplugin.c b/gst/gstplugin.c
index 1a62cf363f..d6a9b760b0 100644
--- a/gst/gstplugin.c
+++ b/gst/gstplugin.c
@@ -1708,15 +1708,15 @@ gst_plugin_ext_dep_equals (GstPluginDep * dep, const gchar ** env_vars,
 /**
  * gst_plugin_add_dependency:
  * @plugin: a #GstPlugin
- * @env_vars: NULL-terminated array of environment variables affecting the
+ * @env_vars: (allow-none): NULL-terminated array of environment variables affecting the
  *     feature set of the plugin (e.g. an environment variable containing
  *     paths where to look for additional modules/plugins of a library),
  *     or NULL. Environment variable names may be followed by a path component
  *      which will be added to the content of the environment variable, e.g.
  *      "HOME/.mystuff/plugins".
- * @paths: NULL-terminated array of directories/paths where dependent files
- *     may be.
- * @names: NULL-terminated array of file names (or file name suffixes,
+ * @paths: (allow-none): NULL-terminated array of directories/paths where dependent files
+ *     may be, or NULL.
+ * @names: (allow-none): NULL-terminated array of file names (or file name suffixes,
  *     depending on @flags) to be used in combination with the paths from
  *     @paths and/or the paths extracted from the environment variables in
  *     @env_vars, or NULL.
@@ -1779,14 +1779,14 @@ gst_plugin_add_dependency (GstPlugin * plugin, const gchar ** env_vars,
 /**
  * gst_plugin_add_dependency_simple:
  * @plugin: the #GstPlugin
- * @env_vars: one or more environment variables (separated by ':', ';' or ','),
+ * @env_vars: (allow-none): one or more environment variables (separated by ':', ';' or ','),
  *      or NULL. Environment variable names may be followed by a path component
  *      which will be added to the content of the environment variable, e.g.
  *      "HOME/.mystuff/plugins:MYSTUFF_PLUGINS_PATH"
- * @paths: one ore more directory paths (separated by ':' or ';' or ','),
+ * @paths: (allow-none): one ore more directory paths (separated by ':' or ';' or ','),
  *      or NULL. Example: "/usr/lib/mystuff/plugins"
- * @names: one or more file names or file name suffixes (separated by commas),
- *   or NULL
+ * @names: (allow-none): one or more file names or file name suffixes (separated by commas),
+ *      or NULL
  * @flags: optional flags, or #GST_PLUGIN_DEPENDENCY_FLAG_NONE
  *
  * Make GStreamer aware of external dependencies which affect the feature
diff --git a/gst/gsttaglist.c b/gst/gsttaglist.c
index 4df26ce483..5f4a5a1e4a 100644
--- a/gst/gsttaglist.c
+++ b/gst/gsttaglist.c
@@ -454,7 +454,7 @@ gst_tag_lookup (const gchar * tag_name)
  * @type: the type this data is in
  * @nick: human-readable name
  * @blurb: a human-readable description about this tag
- * @func: function for merging multiple values of this tag, or NULL
+ * @func: (allow-none): function for merging multiple values of this tag, or NULL
  *
  * Registers a new tag type for the use with GStreamer's type system. If a type
  * with that name is already registered, that one is used.
@@ -498,7 +498,7 @@ gst_tag_register (const gchar * name, GstTagFlag flag, GType type,
  * @type: the type this data is in
  * @nick: human-readable name or short description (string constant)
  * @blurb: a human-readable description for this tag (string constant)
- * @func: function for merging multiple values of this tag, or NULL
+ * @func: (allow-none): function for merging multiple values of this tag, or NULL
  *
  * Registers a new tag type for the use with GStreamer's type system.
  *
diff --git a/gst/gsttypefind.c b/gst/gsttypefind.c
index 2bf7faa946..c41481058d 100644
--- a/gst/gsttypefind.c
+++ b/gst/gsttypefind.c
@@ -42,7 +42,7 @@ G_DEFINE_POINTER_TYPE (GstTypeFind, gst_type_find);
 
 /**
  * gst_type_find_register:
- * @plugin: A #GstPlugin, or NULL for a static typefind function
+ * @plugin: (allow-none): A #GstPlugin, or NULL for a static typefind function
  * @name: The name for registering
  * @rank: The rank (or importance) of this typefind function
  * @func: The #GstTypeFindFunction to use
@@ -159,7 +159,7 @@ gst_type_find_suggest (GstTypeFind * find, guint probability, GstCaps * caps)
  * @find: The #GstTypeFind object the function was called with
  * @probability: The probability in percent that the suggestion is right
  * @media_type: the media type of the suggested caps
- * @fieldname: first field of the suggested caps, or NULL
+ * @fieldname: (allow-none): first field of the suggested caps, or NULL
  * @...: additional arguments to the suggested caps in the same format as the
  *     arguments passed to gst_structure_new() (ie. triplets of field name,
  *     field GType and field value)
diff --git a/gst/gstutils.c b/gst/gstutils.c
index 53a99d8f6e..454c7facae 100644
--- a/gst/gstutils.c
+++ b/gst/gstutils.c
@@ -2166,7 +2166,7 @@ gst_element_query_position (GstElement * element, GstFormat format,
  * gst_element_query_duration:
  * @element: a #GstElement to invoke the duration query on.
  * @format: the #GstFormat requested
- * @duration: (out): A location in which to store the total duration, or NULL.
+ * @duration: (out) (allow-none): A location in which to store the total duration, or NULL.
  *
  * Queries an element for the total stream duration.
  *
@@ -2531,7 +2531,7 @@ gst_pad_proxy_query_caps (GstPad * pad, GstQuery * query)
  * gst_pad_query_position:
  * @pad: a #GstPad to invoke the position query on.
  * @format: the #GstFormat requested
- * @cur: (out): A location in which to store the current position, or NULL.
+ * @cur: (out) (allow-none): A location in which to store the current position, or NULL.
  *
  * Queries a pad for the stream position.
  *
diff --git a/libs/gst/base/gstcollectpads.c b/libs/gst/base/gstcollectpads.c
index f3d0af903f..e9cababa4a 100644
--- a/libs/gst/base/gstcollectpads.c
+++ b/libs/gst/base/gstcollectpads.c
@@ -484,7 +484,7 @@ gst_collect_pads_set_query_function (GstCollectPads * pads,
 * @pads: the collectpads to use
 * @cdata: collect data of corresponding pad
 * @buf: buffer being clipped
-* @outbuf: output buffer with running time, or NULL if clipped
+* @outbuf: (allow-none): output buffer with running time, or NULL if clipped
 * @user_data: user data (unused)
 *
 * Convenience clipping function that converts incoming buffer's timestamp
diff --git a/libs/gst/base/gsttypefindhelper.c b/libs/gst/base/gsttypefindhelper.c
index 42c058a1a1..f4a458ed85 100644
--- a/libs/gst/base/gsttypefindhelper.c
+++ b/libs/gst/base/gsttypefindhelper.c
@@ -246,7 +246,7 @@ helper_find_get_length (gpointer data)
 /**
  * gst_type_find_helper_get_range:
  * @obj: A #GstObject that will be passed as first argument to @func
- * @parent: the parent of @obj or NULL
+ * @parent: (allow-none): the parent of @obj or NULL
  * @func: (scope call): A generic #GstTypeFindHelperGetRangeFunction that will
  *        be used to access data at random offsets when doing the typefinding
  * @size: The length in bytes
@@ -480,7 +480,7 @@ buf_helper_find_suggest (gpointer data, GstTypeFindProbability probability,
 
 /**
  * gst_type_find_helper_for_data:
- * @obj: object doing the typefinding, or NULL (used for logging)
+ * @obj: (allow-none): object doing the typefinding, or NULL (used for logging)
  * @data: (in) (transfer none): a pointer with data to typefind
  * @size: (in) (transfer none): the size of @data
  * @prob: (out) (allow-none): location to store the probability of the found
@@ -552,7 +552,7 @@ gst_type_find_helper_for_data (GstObject * obj, const guint8 * data, gsize size,
 
 /**
  * gst_type_find_helper_for_buffer:
- * @obj: object doing the typefinding, or NULL (used for logging)
+ * @obj: (allow-none): object doing the typefinding, or NULL (used for logging)
  * @buf: (in) (transfer none): a #GstBuffer with data to typefind
  * @prob: (out) (allow-none): location to store the probability of the found
  *     caps, or #NULL
diff --git a/libs/gst/base/gsttypefindhelper.h b/libs/gst/base/gsttypefindhelper.h
index 805192947f..9447f9ba5a 100644
--- a/libs/gst/base/gsttypefindhelper.h
+++ b/libs/gst/base/gsttypefindhelper.h
@@ -44,7 +44,7 @@ GstCaps * gst_type_find_helper_for_extension (GstObject * obj,
 /**
  * GstTypeFindHelperGetRangeFunction:
  * @obj: a #GstObject that will handle the getrange request
- * @parent: the parent of @obj or NULL
+ * @parent: (allow-none): the parent of @obj or NULL
  * @offset: the offset of the range
  * @length: the length of the range
  * @buffer: a memory location to hold the result buffer