SDK - Skip attributes with missing values during PipelineMeta seriali…

…zation

sdk/python/kfp/dsl/_metadata.py

@@ -93,10 +93,16 @@ def __init__(self,
     self.default = default
 
   def to_dict(self):
-    return {'name': self.name,
-            'description': self.description,
-            'type': self.param_type.to_dict_or_str(),
-            'default': self.default}
+    result = {}
+    if self.name:
+      result['name'] = self.name
+    if self.description:
+      result['description'] = self.description
+    if self.param_type:
+      result['type'] = self.param_type.to_dict_or_str()
+    if self.default:
+      result['default'] = self.default
+    return result
 
 class ComponentMeta(BaseMeta):
   def __init__(
@@ -112,11 +118,16 @@ def __init__(
     self.outputs = [] if outputs is None else outputs
 
   def to_dict(self):
-    return {'name': self.name,
-            'description': self.description,
-            'inputs': [ input.to_dict() for input in self.inputs ],
-            'outputs': [ output.to_dict() for output in self.outputs ]
-            }
+    result = {}
+    if self.name:
+      result['name'] = self.name
+    if self.description:
+      result['description'] = self.description
+    if self.inputs:
+      result['inputs'] = [input.to_dict() for input in self.inputs]
+    if self.outputs:
+      result['outputs'] = [output.to_dict() for output in self.outputs]
+    return result
 
 # Add a pipeline level metadata calss here.
 # If one day we combine the component and pipeline yaml, ComponentMeta and PipelineMeta will become one, too.
@@ -132,10 +143,14 @@ def __init__(
     self.inputs = [] if inputs is None else inputs
 
   def to_dict(self):
-    return {'name': self.name,
-            'description': self.description,
-            'inputs': [ input.to_dict() for input in self.inputs ]
-            }
+    result = {}
+    if self.name:
+      result['name'] = self.name
+    if self.description:
+      result['description'] = self.description
+    if self.inputs:
+      result['inputs'] = [input.to_dict() for input in self.inputs]
+    return result
 
 def _annotation_to_typemeta(annotation):
   '''_annotation_to_type_meta converts an annotation to an instance of TypeMeta