diff --git a/redisgraph/edge.py b/redisgraph/edge.py
index 34c4b67..3dbcf69 100644
--- a/redisgraph/edge.py
+++ b/redisgraph/edge.py
@@ -10,11 +10,14 @@ def __init__(self, src_node, relation, dest_node, edge_id=None, properties=None)
         """
         Create a new edge.
         """
-        assert src_node is not None and dest_node is not None
+        if not (src_node and dest_node):
+            # NOTE(bors-42): It makes sense to change AssertionError to
+            #                ValueError here
+            raise AssertionError("Both src_node & dest_node must be provided")
 
         self.id = edge_id
-        self.relation = '' or relation
-        self.properties = {} or properties
+        self.relation = relation or ''
+        self.properties = properties or {}
         self.src_node = src_node
         self.dest_node = dest_node
 
diff --git a/redisgraph/graph.py b/redisgraph/graph.py
index bd05a07..7f15c39 100644
--- a/redisgraph/graph.py
+++ b/redisgraph/graph.py
@@ -93,11 +93,12 @@ def add_node(self, node):
 
     def add_edge(self, edge):
         """
-        Addes an edge to the graph.
+        Adds an edge to the graph.
         """
+        if not (self.nodes[edge.src_node.alias]
+                and self.nodes[edge.dest_node.alias]):
+            raise AssertionError("Both edge's end must be in the graph")
 
-        # Make sure edge both ends are in the graph
-        assert self.nodes[edge.src_node.alias] is not None and self.nodes[edge.dest_node.alias] is not None
         self.edges.append(edge)
 
     def commit(self):
@@ -128,12 +129,13 @@ def flush(self):
         self.edges = []
 
     def build_params_header(self, params):
-        assert type(params) == dict
+        if not isinstance(params, dict):
+            raise TypeError("'params' must be a dict")
         # Header starts with "CYPHER"
         params_header = "CYPHER "
         for key, value in params.items():
             # If value is string add quotation marks.
-            if type(value) == str:
+            if isinstance(value, str):
                 value = quote_string(value)
             # Value is None, replace with "null" string.
             elif value is None:
@@ -189,7 +191,6 @@ def execution_plan(self, query, params=None):
         Get the execution plan for given query,
         GRAPH.EXPLAIN returns an array of operations.
         """
-
         if params is not None:
             query = self.build_params_header(params) + query