Fix unsafe None checks (#449)

* None checks added for constructors

* Changes in None check and resolve comments

Author: jayanthchandra

tensornetwork/network_components.py

@@ -69,7 +69,7 @@ def __init__(self,
     """
 
     self.is_disabled = False
-    if not name:
+    if name is None:
       name = '__unnamed_node__'
     else:
       if not isinstance(name, str):
@@ -554,7 +554,7 @@ def __init__(self,
       #always use the `Node`'s backend
       backend = tensor.backend
       tensor = tensor.tensor
-    if not backend:
+    if backend is None:
       backend = get_default_backend()
     if isinstance(backend, BaseBackend):
       backend_obj = backend
@@ -715,7 +715,7 @@ def __init__(self,
         backend with a tf.Dtype=tf.floa32, `dtype` has to be `np.float32`.
     """
 
-    if not backend:
+    if backend is None:
       backend = get_default_backend()
     backend_obj = backend_factory.get_backend(backend)
 
@@ -924,7 +924,7 @@ def __init__(self,
       raise ValueError(
           "node2 and axis2 must either be both None or both not be None")
     self.is_disabled = False
-    if not name:
+    if name is None:
       name = '__unnamed_edge__'
     else:
       if not isinstance(name, str):