live: hw_inventory: fix empty memory bank bug

When a client's hardware presents an empty memory bank and invalid call
to _bytes_to_human is performed because None is passed as a parameter.

	size = _bytes_to_human(obj.get('size', None))

Fix this by checking if 'size' is present in the JSON output from lshw.
If size is present then map the bytes to a human readable string using
_bytes_to_human, if no size is present then use 'Empty slot' to indicate
that the memory bank is not being used.

src/utils/hw_inventory.py

@@ -64,7 +64,7 @@ class HardwareInventory():
 def _bytes_to_human(size):
     suffixes = ['B', 'MiB', 'GiB', 'TiB']
     if type(size) is not int:
-        raise TypeError('Invalid type')
+        raise TypeError(f'Invalid type in _bytes_to_human, got: {size} {type(size)}')
     for exponent, suffix in enumerate(suffixes, start=1):
         conv = size / (1024**exponent)
         if conv < 1024:
@@ -106,11 +106,14 @@ def _process_core_cpu(inventory, obj):
 
 def _process_core_mem_bank(inventory, obj):
     slot = obj.get('slot', 'Unknown slot')
-    size = _bytes_to_human(obj.get('size', None))
-    if size:
-        mem = ' '.join([obj.get('vendor', 'Unknown vendor'), obj.get('product', 'Unknown product'), size, f'({slot})'])
-        mem_elem = HardwareElement(HardwareType.MEMORY, mem)
-        inventory.add_element(mem_elem)
+    if 'size' in obj:
+        size = obj['size']
+        human_size = _bytes_to_human(size)
+        mem = ' '.join([obj.get('vendor', 'Unknown vendor'), obj.get('product', 'Unknown product'), human_size, f'({slot})'])
+    else:
+        mem = ' '.join([obj.get('vendor', 'Unknown vendor'), obj.get('product', 'Unknown product'), 'Empty slot', f'({slot})'])
+    mem_elem = HardwareElement(HardwareType.MEMORY, mem)
+    inventory.add_element(mem_elem)
 
 
 def _process_core_mem(inventory, obj):