Dumping OVS flows of a NetworkPolicy

Fixes #3306.

This commit fixes the nil pointer dereferrence error while dumping the ovsflows of NetworkPolicy.

Signed-off-by: Pulkit Jain <jainpu@vmware.com>

pkg/agent/openflow/network_policy.go

@@ -1455,6 +1455,11 @@ func (c *client) GetNetworkPolicyFlowKeys(npName, npNamespace string) []string {
 
 	for _, conjObj := range c.policyCache.List() {
 		conj := conjObj.(*policyRuleConjunction)
+		// If the NetworkPolicyReference in the policyRuleConjunction is nil then that entry in client's
+		// policyCache should be ignored because here we need to dump flows of NetworkPolicy.
+		if conj.npRef == nil {
+			continue
+		}
 		if conj.npRef.Name == npName && conj.npRef.Namespace == npNamespace {
 			// There can be duplicated flows added due to conjunctive matches
 			// shared by multiple policy rules (clauses).