Removing an empty entry rule by using QgsRuleBasedRenderer without affect other rules filled in PyQGIS?

Question

I create rules with this code but it creates one more but without data and when using root_rule.removeChildAt (0) it deletes a correct one.

layer = iface.activeLayer()
symbol = QgsSymbol.defaultSymbol(layer.geometryType())
renderer = QgsRuleBasedRenderer(symbol)

def rule_based_style(layer, symbol, renderer, label, expression, color):
    root_rule = renderer.rootRule()
    rule = root_rule.children()[0].clone()
    rule.setLabel(label)
    rule.setFilterExpression(expression)
    rule.symbol().setColor(QColor(color))
    # append the rule to the list of rules
    root_rule.appendChild(rule)
    #delete the default rule[![remove 2 rules][1]][1]
    root_rule.removeChildAt(0)
    layer.setRenderer(renderer)    
    layer.triggerRepaint()

    iface.layerTreeView().refreshLayerSymbology(layer.id())

#rule_based_style(layer, symbol, renderer, 'Para Campo', ' \"REVISION\" = \'Para Campo\' ', 'yellow')
rule_based_style(layer, symbol, renderer, 'Para Campo', ' \"REVISION\" = \'Para Campo\' ', 'yellow')
rule_based_style(layer, symbol, renderer, 'De Campo NA NULL', ' \"REVISION\" = \'De Campo\' or \"REVISION\" = \'De Campo\' or \"REVISION\" IS NULL ', 'green')

Answer 1

• First, use the method to add rules to renderer and don't use removeChildAt(0) within the method.
• After adding the rules, remove the first child of renderer.
• Then set layer renderer.
• You don't need to define parameters for layer, symbol and renderer in method definition.
• You don't need " in expression for field names.

layer = iface.activeLayer()
symbol = QgsSymbol.defaultSymbol(layer.geometryType())
renderer = QgsRuleBasedRenderer(symbol)

def add_rule_to_renderer(label, expression, color):
    rule = renderer.rootRule().children()[0].clone()
    rule.setLabel(label)
    rule.setFilterExpression(expression)
    rule.symbol().setColor(QColor(color))
    renderer.rootRule().appendChild(rule)

add_rule_to_renderer('Para Campo', "REVISION='Para Campo'", 'yellow')
add_rule_to_renderer('De Campo NA NULL', "REVISION='De Campo' or REVISION IS NULL", 'green')

# remove first child
renderer.rootRule().removeChildAt(0)

layer.setRenderer(renderer)    
layer.triggerRepaint()

iface.layerTreeView().refreshLayerSymbology(layer.id())